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Polynomials

Class 10th Mathematics Rajasthan Board Solution
Exercise 3.1
  1. 4x2 + 8x Find the zeroes of the following quadratic polynomials and verify the…
  2. 4x2 – 4x + 1 Find the zeroes of the following quadratic polynomials and verify…
  3. 6x2 – x – 2 Find the zeroes of the following quadratic polynomials and verify…
  4. x2 – 15 Find the zeroes of the following quadratic polynomials and verify the…
  5. x^{2} - ( root {3}+1 ) x + sqrt{3} Find the zeroes of the following quadratic…
  6. 3x2 – x – 4 Find the zeroes of the following quadratic polynomials and verify…
  7. –3, 2 Find a quadratic polynomial the sum and the product of whose zeroes are…
  8. root {2} , {1}/{3} Find a quadratic polynomial the sum and the product of…
  9. - {1}/{4} , frac {1}/{4} Find a quadratic polynomial the sum and the product…
  10. 0 , root {5} Find a quadratic polynomial the sum and the product of whose…
  11. 4, 1 Find a quadratic polynomial the sum and the product of whose zeroes are…
  12. 1, 1 Find a quadratic polynomial the sum and the product of whose zeroes are…
  13. If sum of squares of zeroes of quadratic polynomial f(x) = x2 – 8x + k is 40,…
Exercise 3.2
  1. f(x) = 3x2 +x2 + 2x +5, g(x) = 1+2x + x2 Find the quotient and the remainder on…
  2. f(x) = x3 – 3x2 + 5x – 3, g(x) = x2 – 2 Find the quotient and the remainder on…
  3. f(x) = x3 – 6x2 + 11x – 6, g(x) = x + 2 Find the quotient and the remainder on…
  4. f(x) = 9x4 – 4x2 + 4, g(x) = 3x2 + x – 1 Find the quotient and the remainder on…
  5. g(x) = x2 + 3x + 1, f(x) = 3x4 + 5x3 – 7x2 + 2x + 2 Dividing the first…
  6. g(t) = t2 – 3, f(t) = 2t4 + 3t3 – 2t2 – 9t – 12 Dividing the first polynomial,…
  7. g(x) = x3 – 3x + 1, f(x) = x5 – 4x3 + x2 + 3x + 1 Dividing the first…
  8. f (x) = 2x^{4} - 3x^{3} - 3x^{2} + 6x-2 root {2} - sqrt{2} With the following…
  9. f (x) = x^{4} - 6x^{3} - 26x^{2} + 138x-35 2 plus or minus root {3} With the…
  10. f(x) = x3 + 13x2 + 32x + 20; –2 With the following polynomials their zeroes are…
  11. On dividing the polynomial f(x) = x3 – 3x2 + x + 2 by the polynomial g(x),…
Exercise 3.3
  1. x(x + 1) + 8 = (x + 2) (x – 2) Check whether the following are quadratic…
  2. (x + 2)3 = x3 – 4 Check whether the following are quadratic equations:…
  3. x3 + 3x + 1 = (x – 2)2 Check whether the following are quadratic equations:…
  4. x + {1}/{x} + x^{2} , x not equal 0 Check whether the following are quadratic…
  5. 2x2 – 5x + 3 = 0 Solve the following equations by factorization method:…
  6. 9x2 – 3x – 2 = 0 Solve the following equations by factorization method:…
  7. root {3}x^{2} + 10x+7 sqrt{3} = 0 Solve the following equations by…
  8. x2 – 8x + 16 = 0 Solve the following equations by factorization method:…
  9. {1}/{x-2} + frac {2}/{x-1} = frac {6}/{x} x not equal 1 , 2 Solve the following…
  10. 100x2 – 20x + 1 = 0 Solve the following equations by factorization method:…
  11. 3x^{2} - 2 root {6}x+2 = 0 Solve the following equations by factorization…
  12. x2 + 8x + 7 Solve the following equations by factorization method:…
  13. {x+3}/{x+2} = frac {3x-7}/{2x-3} Solve the following equations by factorization…
  14. abx2 + (b2 – ac)x – bc = 0 Solve the following equations by factorization…
Exercise 3.4
  1. 3x2 – 5x + 2 = 0 Solve the following quadratic equations by the method of…
  2. 5x2 – 6x – 2 = 0 Solve the following quadratic equations by the method of…
  3. 4x2 + 3x + 5 = 0 Solve the following quadratic equations by the method of…
  4. 4x^{2} + 4 root {3}x+3 = 0 Solve the following quadratic equations by the…
  5. 2x2 + x – 4 = 0 Solve the following quadratic equations by the method of…
  6. 2x2 + x + 4 = 0 Solve the following quadratic equations by the method of…
  7. 4x2 + 4bx – (a2 – b2) = 0 Solve the following quadratic equations by the method…
  8. 2x^{2} - 2 root {2}+1 = 0 Find the root of the following quadratic equations,…
  9. 9x2 + 7x – 2 = 0 Find the root of the following quadratic equations, if they…
  10. x + {1}/{x} = 3 , x not equal 0 Find the root of the following quadratic…
  11. root {2}x^{2} + 7x+5 sqrt{2} = 0 Find the root of the following quadratic…
  12. x2 + 4x + 5 = 0 Find the root of the following quadratic equations, if they…
  13. {1}/{x} - frac {1}/{x-2} = 3 , x not equal 0 , 2 Find the root of the following…
  14. Find two consecutive odd positive integers, sum of whose squares is 290.…
  15. The difference of squares of two numbers is 45 and the square of the smaller…
  16. Divide 16 into two parts such that two times the square of the larger part is…
Exercise 3.5
  1. 2x2 – 3x + 5 = 0 Find the nature of the roots of the following quadratic…
  2. 2x2 – 4x + 3 = 0 Find the nature of the roots of the following quadratic…
  3. 2x2 + x – 1 = 0 Find the nature of the roots of the following quadratic…
  4. x2 – 4x + 4 = 0 Find the nature of the roots of the following quadratic…
  5. 2x2 + 5x + 5 = 0 Find the nature of the roots of the following quadratic…
  6. 3x^{2} - 2x + {1}/{3} = 0 Find the nature of the roots of the following…
  7. kx(x – 2) + 6 = 0 Find that value of k in the following quadratic equation…
  8. x2 – 2(k + 1)x + k2 = 0 Find that value of k in the following quadratic…
  9. 2x2 + kx + 3 = 0 Find that value of k in the following quadratic equation whose…
  10. (k + 1)x2 – 2(k –1)x + 1 = 0 Find that value of k in the following quadratic…
  11. (k + 4) x2 + (k + 1) x + 1 = 0 Find that value of k in the following quadratic…
  12. kx2 – 5x + k = 0 Find that value of k in the following quadratic equation whose…
  13. kx2 + 2x + 1 = 0 Find these values of k for which the roots of the following…
  14. kx2 + 6x + 1 Find these values of k for which the roots of the following…
  15. x2 – kx + 9 = 0 Find these values of k for which the roots of the following…
  16. Find those values of k for which the roots of the equation x2 + 5kx + 16 = 0 are…
  17. If the roots of the quadratic equation (b – c)x2 + (c – a)x + (a – b) = 0 are…
Exercise 3.6
  1. 24x2yz and 27x4y2z2 Find the lowest common multiple of the following…
  2. x2 – 3x + 2 and x4 + x3 – 6x2 Find the lowest common multiple of the following…
  3. (iii) 2x2 – 8 and x2 – 5x + 6 Find the lowest common multiple of the following…
  4. x2 – 1; (x2 + 1) (x + 1) and x2 + x –1 Find the lowest common multiple of the…
  5. 18(6x4 + x3 – x2) and 45(2x6 + 3x5 + x4) Find the lowest common multiple of the…
  6. Find the highest common factor of the following expressions:(i) a3b4, ab5,…
  7. If u(x) = (x – 1)2 and v(x) = (x2 – 1) the check the true of the relation LCM ×…
  8. The product of two expressions is (x – 7) (x2 + 8x + 12). If the HCF of these…
  9. The HCF and LCM of two quadratic expressions are respectively (x – 5) and x3 –…
Miscellaneous Exercise 3
  1. If one zero of the polynomial f(x) = 5x2 + 13x + k is reciprocal of the other…
  2. The zeroes of the polynomials x2 – x – 6 are:
  3. If one zero of the polynomial 2x2 + x + k is 3 then the value of k will be:…
  4. If α, β, are the zeroes of the polynomial x2 – p(x + 1) – c such that (α + 1) (β…
  5. If the roots of the quadratic equation x2 – kx + 4 = 0 are equal then the value…
  6. If x = 1 is a common root of the equations ax2 + ax + 3 = 0 and x2 + x + b = 0…
  7. The discriminant of the quadratic equation 3 root {3}x^{2} + 10x + sqrt{3} = 0…
  8. The nature of roots of the quadratic equation 4x2 – 12x – 9 = 0 is :…
  9. The HCF of expression 8a2b2c and 20ab3c2 is:
  10. The LCM of expressions x2 – 1 and x2 +2x + 1 is :
  11. If LCM of expressions 6x2y4 and 10xy2 is 30x2y4 then HCF will be:…
  12. Write Shridharacharya Formula of finding the roots of the quadratic equation…
  13. Writing the general form of the discriminant of the equation ax2 + by + c = 0…
  14. Find the zeroes of the quadratic polynomial 2x2 – 8x + 6 and examine the truth…
  15. If α and β are the zeroes of the quadratic polynomial f(x) = x2 – px + q then…
  16. If the polynomial x4– 6x3 + 16x + 10 is divided by another polynomial x2 – 2x +…
  17. The area of a rectangular plot is 528 m2. The length of the plot (in m) is 1…
  18. Solve the quadratic equation x2 + 4x – 5 = 0 by the method of completing the…
  19. {1}/{x} = frac {1}/{x-2} = 3 , x not equal 0 , 2 Solve the following equation…
  20. {1}/{x-1} - frac {1}/{x+5} = frac {6}/{7} , x not equal 1 ,-5 Solve the…
  21. x - {1}/{x} = 3 , x not equal 0 Solve the following equation by…
  22. {1}/{x+4} - frac {1}/{x-7} = frac {11}/{30} x not equal -4 , 7 Solve the…
  23. If one root of a quadratic equation 2x2 + px – 15 = 0 is –5 and the root of the…
  24. p2x2 + (p2 – q2)x – q2 = 0 Solve the following quadratic equations by using…
  25. 9x2 – 9(a + b)x + (2a2 + 5ab + 2b2) = 0 Solve the following quadratic…
  26. The LCM and HCF of two quadratic expressions are respectively x3 – 7x + 6 and…
  27. The LCM of two polynomials in x3 – 6x2 + 3x + 10 and HCF is (x + 1). If one…

Exercise 3.1
Question 1.

Find the zeroes of the following quadratic polynomials and verify the relationship between the zeroes and the coefficients.

4x2 + 8x


Answer:

To find the zeros of the polynomial let us first solve the polynomial by equating it to zero. Factorizing the given polynomial

4x2 + 8x = 0


4x(x + 8) = 0


4x = 0 or x + 8 = 0


Now solving the first part,


4x = 0


x = 0/4


x = 0


Now solving the second part,


x + 8 = 0


x = -8


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 4, b = 8, c = 0


Sum of zeroes = -b / a


= -8 / 4


= -2


Product of zeroes = c / a


= 0 / 4


= 0



Question 2.

Find the zeroes of the following quadratic polynomials and verify the relationship between the zeroes and the coefficients.

4x2 – 4x + 1


Answer:

To find the zeros of the polynomial let us first solve the polynomial by equating it to zero. Factorizing the given polynomial

4x2 – 4x + 1 = 0


To factorize the polynomial we have,


Sum of the value should be equal = -4


Product should be equal to = 4 × 1


= 4


So two numbers are -2, -2


4x2 – 2x – 2x + 1 = 0


2x(2x – 1) – 1(2x – 1) = 0


(2x-1)(2x-1) = 0


2x-1 = 0 or 2x-1 = 0


Both the parts are same.


Solving them,


2x-1 = 0


2x = 1


x = 1/2


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 4, b = -4, c = 1


Sum of zeroes = -b / a


= - (-4) / 4


= 1


Product of zeroes = c / a


= 1 / 4


= 1/4



Question 3.

Find the zeroes of the following quadratic polynomials and verify the relationship between the zeroes and the coefficients.

6x2 – x – 2


Answer:

To find the zeros of the polynomial let us first solve the polynomial by equating it to zero. Factorizing the given polynomial

6x2 – x - 2 = 0


To factorize the polynomial we have,


Sum of the value should be equal = -1


Product should be equal to = 6 × (-2)


= -12


So two numbers are -4, 3


6x2 – 4x + 3x - 2 = 0


2x (3x – 2) + 1(3x – 2) = 0


(2x+1)(3x-2) = 0


2x+1 = 0 or 3x-2 = 0


Now Solving first part,


2x+1 = 0


2x = -1


x = -1/2


Now solving the second part,


3x-2 = 0


3x = 2


x = 2/3


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 6, b = -1, c = -2


Sum of zeroes = -b / a


= - (-1) / 6


= 1/6


Product of zeroes = c / a


= -2 / 6


= -1/3



Question 4.

Find the zeroes of the following quadratic polynomials and verify the relationship between the zeroes and the coefficients.

x2 – 15


Answer:

To find the zeros of the polynomial let us first solve the polynomial by equating it to zero. Factorizing the given polynomial

x2 – 15 = 0


x2 = 15


x = √15


When we take square root on both sides, we get two values of a variable


Thus x = +√15 and x = -√15


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 1, b = 0, c = -15


Sum of zeroes = -b / a


= 0 / 4


= 0


Product of zeroes = c / a


= -15 / 1


= -15



Question 5.

Find the zeroes of the following quadratic polynomials and verify the relationship between the zeroes and the coefficients.




Answer:

To find the zeros of the polynomial let us first solve the polynomial by equating it to zero. Factorizing the given polynomial

x2 – (√3 + 1)x + √3 = 0


To factorize the polynomial we have,


Sum of the value should be equal = -(√3 + 1)


Product should be equal to = 1 × √3


= √3


x2 – [2(√3 + 1)x]/2 + √3 = 0


x2 - 2(√3 + 1)x/2 + (√3 + 1)2/22 - (√3 + 1)2/22 + √3 = 0


[x - (√3 + 1)/2]2 - (3 + 1 + 2√3)/4 + √3 = 0


[x - (√3 + 1)/2]2 = (3 + 1 + 2√3 - 4√3)/4


[x - (√3 + 1)/2]2 = (√3 - 1)2/22


[x - (√3 + 1)/2] = ± (√3 - 1)/2


Solving for positive value,


x = (√3 - 1)/2 + (√3 + 1)/2


x = (√3 - 1 + √3 + 1)/2


x = 2√3/2 = √3


Solving for negative value,


x = -(√3 - 1)/2 + (√3 + 1)/2


x = (-√3 + 1 + √3 + 1)/2


x = 2/2 = 1


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 1, b = - (√3 + 1), c = √3


Sum of zeroes = -b / a


= (√3 + 1) / 1


= √3 + 1


Product of zeroes = c / a


= √3 / 1


= √3



Question 6.

Find the zeroes of the following quadratic polynomials and verify the relationship between the zeroes and the coefficients.

3x2 – x – 4


Answer:

To find the zeros of the polynomial let us first solve the polynomial by equating it to zero. Factorizing the given polynomial

3x2 – x - 4 = 0


To factorize the polynomial we have,


Sum of the value should be equal = -1


Product should be equal to = 3 × (-4)


= -12


So two numbers are -4, 3


3x2 – 4x + 3x - 4 = 0


3x (x + 1) -4 (x + 1) = 0


(3x - 4)(x + 1) = 0


3x - 4 = 0 or x + 1 = 0


Now solving first part,


3x-4 = 0


3x = 4


x = 4/3


Now solving the second part,


x + 1 = 0


x = -1


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 3, b = -1, c = -4


Sum of zeroes = -b / a


= - (-1) / 3


= 1/3


Product of zeroes = c / a


= -4 / 3


= -4/3



Question 7.

Find a quadratic polynomial the sum and the product of whose zeroes are respectively the given numbers.

–3, 2


Answer:

Let the two zeroes be a and b.

The generalized form of the quadratic equation with sum and product of zeroes a and b is as follows:


ax2 + bx + c = 0 ………………… (i)


Now in this case


∴ a + b = -b/a = -3


∴ ab = c / a = 2


If a = k where k is any real number


b = 3k ………………… (ii)


c = 2k ………………… (iii)


Put values from (ii) and (iii) in (i)


kx2 + 3kx + 2k = 0


k (x2 + 3x + 2) = 0


Therefore the quadratic equation is as follows:


x2 + 3x + 2 = 0



Question 8.

Find a quadratic polynomial the sum and the product of whose zeroes are respectively the given numbers.




Answer:

Let the two zeroes be a and b.

The generalized form of the quadratic equation with sum and product of zeroes a and b is as follows:


ax2 + bx + c = 0 ………………… (i)


Now in this case


∴ a + b = -b/a = √2


∴ ab = c/a = 1/3


If a = k, where k is any real number


b = -√2k ………………… (ii)


c = k/3 ………………… (iii)


Put values from (ii) and (iii) in (i)


kx2 - √2kx + k/3 = 0


3kx2 - 3√2kx + k = 0


k (x2 - 3√2x + 1) = 0


Therefore the quadratic equation is as follows:


(x2 - 3√2x + 1) = 0



Question 9.

Find a quadratic polynomial the sum and the product of whose zeroes are respectively the given numbers.




Answer:

Let the two zeroes be a and b.

The generalized form of the quadratic equation with sum and product of zeroes a and b is as follows:


ax2 + bx + c = 0 ………………… (i)


Now in this case


∴ a + b = -b/a = -1/4


∴ ab = 1/4 ………………… (iii)


If a = k, where k is any real number


b = k/4………………… (ii)


c = k/4 ………………… (iii)


Put values from (ii) and (iii) in (i)


kx2 + k/4x + k/4 = 0


4kx2 + kx + k = 0


k (4x2 + x + 1) = 0


Therefore the quadratic equation is as follows:


(4x2 + x + 1) = 0



Question 10.

Find a quadratic polynomial the sum and the product of whose zeroes are respectively the given numbers.




Answer:

Let the two zeroes be a and b.

The generalized form of the quadratic equation with sum and product of zeroes a and b is as follows:


ax2 + bx + c = 0 ………………… (i)


Now in this case


∴ a + b = -b/a = 0


∴ ab = c/a = √5


If a = k, where k is any real number,


b = 0 ………………… (ii)


c = √5k ………………… (iii)


Put values from (ii) and (iii) in (i)


kx2 + (0)x + (√5k) = 0


k (x2 + √5) = 0


Therefore the quadratic equation is as follows:


x2 + √5 = 0



Question 11.

Find a quadratic polynomial the sum and the product of whose zeroes are respectively the given numbers.

4, 1


Answer:

Let the two zeroes be a and b.

The generalized form of the quadratic equation with sum and product of zeroes a and b is as follows:


ax2 + bx + c = 0 ………………… (i)


Now in this case


∴ a + b = -b/a = 4 ………………… (ii)


∴ ab = c/a = 1 ………………… (ii)


If a = k, where k is any real number


b = -4k


c = k


Put values from (ii) and (iii) in (i)


kx2 – 4kx + k = 0


k (x2 – 4x + 1) = 0


Therefore the quadratic equation is as follows:


(x2 – 4x + 1) = 0



Question 12.

Find a quadratic polynomial the sum and the product of whose zeroes are respectively the given numbers.

1, 1


Answer:

Let the two zeroes be a and b.

The generalized form of the quadratic equation with sum and product of zeroes a and b is as follows:


ax2 + bx + c = 0 ………………… (i)


Now in this case


∴ a + b = -b/a = 1


∴ ab = c/a =1


If a = k, where k is any real integer,


b = -k ………………… (ii)


c = k ………………… (iii)


Put values from (ii) and (iii) in (i)


kx2 – kx + k = 0


k (x2 – x + 1) = 0


Therefore the quadratic equation is as follows:


(x2 – x + 1) = 0



Question 13.

If sum of squares of zeroes of quadratic polynomial f(x) = x2 – 8x + k is 40, the find the value of k.


Answer:

Let the two zeroes be a and b.

Given:


Sum of squares of zeroes is 40


a2 + b2 = 40


The generalized form of the quadratic equation with sum and product of zeroes a and b is as follows:


x2 – (a + b)x + ab = 0 ………………… (i)


a + b = 8


ab = k


We also know that,


(a + b)2 = a2 + b2 + 2ab


a2 + b2 = (a + b) 2 – 2ab


(a + b) 2 – 2ab = 40


(8)2 – 2k= 40


2k = 64 – 40


2k = 24


k = 12


Therefore the value of k = 12




Exercise 3.2
Question 1.

Find the quotient and the remainder on dividing f(x) by using division algorithm.

f(x) = 3x2 +x2 + 2x +5, g(x) = 1+2x + x2


Answer:

The solution is as follows:


Therefore the quotient and remainder are as follows:


Quotient = 3x – 5


Remainder = 9x + 10



Question 2.

Find the quotient and the remainder on dividing f(x) by using division algorithm.

f(x) = x3 – 3x2 + 5x – 3, g(x) = x2 – 2


Answer:

The solution is as follows:


Quotient = x – 3


Remainder = 7x – 9



Question 3.

Find the quotient and the remainder on dividing f(x) by using division algorithm.

f(x) = x3 – 6x2 + 11x – 6, g(x) = x + 2


Answer:

The solution is as follows:


Quotient = x2 – 8x + 27


Remainder = -60



Question 4.

Find the quotient and the remainder on dividing f(x) by using division algorithm.

f(x) = 9x4 – 4x2 + 4, g(x) = 3x2 + x – 1


Answer:

The solution is as follows:


Quotient = 3x2 – x


Remainder = -x + 4



Question 5.

Dividing the first polynomial, by the second polynomial, check whether the first polynomial is a factor of the second polynomial:

g(x) = x2 + 3x + 1, f(x) = 3x4 + 5x3 – 7x2 + 2x + 2


Answer:

The solution is as follows:


Since the remainder is zero, it is proved that the first polynomial is the factor of second.



Question 6.

Dividing the first polynomial, by the second polynomial, check whether the first polynomial is a factor of the second polynomial:

g(t) = t2 – 3, f(t) = 2t4 + 3t3 – 2t2 – 9t – 12


Answer:

The solution is as follows:


Since the remainder is zero, it is proved that the first polynomial is the factor of second.



Question 7.

Dividing the first polynomial, by the second polynomial, check whether the first polynomial is a factor of the second polynomial:

g(x) = x3 – 3x + 1, f(x) = x5 – 4x3 + x2 + 3x + 1


Answer:

The solution is as follows:


Since the remainder is not zero, it is proved that the first polynomial is not the factor of second.


Remainder is 9x – 3



Question 8.

With the following polynomials their zeroes are given. Find their all other zeroes:




Answer:

Given that √2 and -√2 are the zeroes of the given polynomial.

So (x - √2) (x + √2) = x2 - 2


The above relation is same as (a + b) (a – b) = a2 – b2


Here a = x and b = √2



The other zeroes are as follows:


2x2 – 3x + 1 = 0


Solving the above quadratic equation.


Sum = -3


Product = 2


So the numbers which satisfy the above condition are -2 and -1


2x2 – 2x - x + 1 = 0


2x(x – 1) – 1(x – 1) = 0


(2x – 1) (x – 1) = 0


Solving the first part,


2x-1 = 0


2x = 1


x = 1/2


Solving the second part,


x – 1 = 0


x = 1


Therefore the other zeroes of the polynomials are 1/2 and 1.



Question 9.

With the following polynomials their zeroes are given. Find their all other zeroes:




Answer:

Given that 2 + √3 and 2 - √3 are the zeroes of the given polynomial.

So (x – (2 + √3)) (x – (2 - √3)) = (x – 2 - √3) (x – 2 + √3)


= x2 – 2x + √3x – 2x + 4 – 2√3 - √3x + 2√3 – 3


= x2 – 4x + 1



The other zeroes are as follows:


x2 – 2x - 35 = 0


Solving the above quadratic equation.


Sum = -2


Product = -35


So the numbers which satisfy the above condition are -7 and 5


x2 – 7x + 5x - 35 = 0


x(x – 7) + 5(x – 7) = 0


(x + 5) (x – 7) = 0


Solving the first part,


x + 5 = 0


x = -5


Solving the second part,


x – 7 = 0


x = 7


Therefore the other zeroes of the polynomials are -5 and 7.



Question 10.

With the following polynomials their zeroes are given. Find their all other zeroes:

f(x) = x3 + 13x2 + 32x + 20; –2


Answer:

Given that -2 is the zero of the polynomial.

So x = -2 which is x + 2 = 0



The other zeroes are as follows:


x2 + 11x + 10 = 0


Solving the above quadratic equation.


Sum = 11


Product = 10


So the numbers which satisfy the above condition are 10 and 1


x2 + 10x + x + 10 = 0


x(x + 1)+ 10(x + 1) = 0


(x + 10) (x + 1) = 0


Solving the first part,


x + 10 = 0


x = -10


Solving the second part,


x + 1 = 0


x = -1


Therefore the other zeroes of the polynomials are -1 and -10.



Question 11.

On dividing the polynomial f(x) = x3 – 3x2 + x + 2 by the polynomial g(x), quotient q(x) and remainder f(x) are respectively obtained as x – 2 and –2x + 4. Find the polynomial g(x).


Answer:

Given:

Dividend = f(x) = x3 – 3x2 + x + 2


Divisor = g(x)


Quotient = x – 2


Remainder = -2x + 4


There is an important relation between dividend, divisor, quotient and remainder which is as follows:


Dividend = Divisor × Quotient + Remainder


x3 – 3x2 + x + 2 = g(x) × (x-2) + (4-2x)


g(x) × (x-2) = x3 – 3x2 + x + 2 – (4 – 2x)


= x3 – 3x2 + x + 2 – 4 + 2x


g(x) × (x-2) = x3 – 3x2 + 3x – 2


Therefore g(x) = (x3 – 3x2 + 3x – 2) / (x-2)



Therefore the g(x) = x2 – x – 1




Exercise 3.3
Question 1.

Check whether the following are quadratic equations:

x(x + 1) + 8 = (x + 2) (x – 2)


Answer:

Let us solve the above equation,

x (x + 1) + 8 = (x + 2) (x – 2)


x2 + x + 8 = (x2 + 2x – 2x – 4)


x2 + x + 8 = x2 – 4


x2 + x + 8 - x2 + 4 = 0


x + 12 = 0


Since on solving the equation we do not get the second power of x which proves that the following set of equation is not quadratic.



Question 2.

Check whether the following are quadratic equations:

(x + 2)3 = x3 – 4


Answer:

Let us solve the above equation,

(x + 2)3 = x3 – 4


x3 + 3x2 × 2 + 3x × 4 + 8 = x3 – 4


x3 + 6x2 + 12x + 8 = x3 – 4


x3 + 6x2 + 12x + 8 - x3 + 4 = 0


6x2 + 12x + 12 = 0


6(x2 + 2x + 1) = 0


x2 + 2x + 1 = 0


Since on solving the equation we do get the second power of x which proves that the following set of equation is quadratic



Question 3.

Check whether the following are quadratic equations:

x3 + 3x + 1 = (x – 2)2


Answer:

Let us solve the above equation,

x3 + 3x + 1 = (x – 2)2


x3 + 3x + 1 = x2 – 2 × 2 × x + 4 …….. [(a-b) 2 = a2 – 2ab + b2]


x3 + 3x + 1 = x2 – 4x + 4


x3 + 3x + 1 - x2 + 4x - 4 = 0


x3 - x2 + 7x - 3 = 0


Since on solving the equation we do get the third power of x along with second power which proves that the following set of equation is not quadratic. A quadratic equation contain the highest power of x which is 2.



Question 4.

Check whether the following are quadratic equations:




Answer:

Let us solve the above equation by equating it to zero,



x2 + 1 + x3 = 0 × x


x2 + 1 + x3 = 0


Since on solving the equation we do get the third power of x along with second power which proves that the following set of equation is not quadratic. A quadratic equation contain the highest power of x which is 2.



Question 5.

Solve the following equations by factorization method:

2x2 – 5x + 3 = 0


Answer:

On factorizing the above equation,

2x2 – 5x + 3 = 0


2x2 – 2x -3x + 3 = 0


2x(x - 1) – 3(x - 1) = 0


(2x - 3) (x - 1) = 0


Solving the first part,


2x - 3 = 0


2x = 3


x = 3/2


Solving the second part,


x – 1 = 0


x = 1



Question 6.

Solve the following equations by factorization method:

9x2 – 3x – 2 = 0


Answer:

On factorizing the above equation,

9x2 – 3x - 2 = 0


9x2 + 3x -6x - 2 = 0


3x(3x + 1) – 2(3x + 1) = 0


(3x - 2) (3x + 1) = 0


Solving the first part,


3x - 2 = 0


3x = 2


x = 2/3


Solving the second part,


3x + 1 = 0


3x = -1


x = -1/3



Question 7.

Solve the following equations by factorization method:




Answer:

On factorizing the above equation,

√3x2 + 10x + 7√3 = 0


√3x2 +3x + 7x + 7√3 = 0


√3x(x + √3) + 7(x + √3) = 0


(√3x + 7) (x + √3) = 0


Solving the first part,


√3x + 7= 0


√3x = -7


x = -7/√3


Solving the second part,


x + √3 = 0


x = -√3



Question 8.

Solve the following equations by factorization method:

x2 – 8x + 16 = 0


Answer:

On factorizing the above equation,

x2 – 8x + 16 = 0


x2 -4x -4x + 16 = 0


x(x - 4) – 4(x - 4) = 0


(x - 4) (x - 4) = 0


Here first and second parts are same,


So x – 4 = 0


x = 4



Question 9.

Solve the following equations by factorization method:




Answer:

On factorizing the above equation,





(3x – 5) × (x) = 6 × (x2 – 3x + 2)


3x2 – 5x = 6x2 – 18x + 6


6x2 – 3x2 – 18x + 5x + 12 = 0


3x2 - 13x + 12 = 0


3x2 - 9x - 4x + 12 = 0


3x(x - 3) -4(x - 3) = 0


(3x – 4)(x - 3) = 0


Solving the first part,


3x – 4 = 0


3x = 4


x = 4/3


Solving the second part,


x – 3 = 0


x = 3



Question 10.

Solve the following equations by factorization method:

100x2 – 20x + 1 = 0


Answer:

On factorizing the above equation,

100x2 – 20x + 1 = 0


100x2 - 10x -10x + 1 = 0


10x(10x - 1) – 1(10x - 1) = 0


(10x - 1) (10x - 1) = 0


Here both the parts are same,


So 10x – 1 = 0


10x = 1


x = 1/10



Question 11.

Solve the following equations by factorization method:




Answer:

On factorizing the above equation,

3x2 – 2√6x + 2 = 0


3x2 - √6x -√6x + 2 = 0


√3x(√3x - √2) – √2(√3x - √2) = 0


(√3x - √2) (√3x - √2) = 0


Here both the roots are equal.


So √3x - √2 = 0


√3x = √2


x = √2 / √3



Question 12.

Solve the following equations by factorization method:

x2 + 8x + 7


Answer:

On factorizing the above equation,

x2 + 8x + 7 = 0


x2 + 7x + x + 7 = 0


x(x + 7) + 1(x + 7) = 0


(x + 7) (x + 1) = 0


Solving the first part,


x + 7= 0


x = -7


Solving the second part,


x + 1 = 0


x = -1



Question 13.

Solve the following equations by factorization method:




Answer:

Cross Multiplying in the above equation,

(x + 3) × (2x – 3) = (3x – 7) × (x + 2)


2x2 – 3x + 6x – 9 = 3x2 + 6x – 7x – 14


2x2 + 3x – 9 = 3x2 – x – 14


3x2 – 2x2 – x - 3x – 14 + 9 = 0


x2 - 4x – 5 = 0


On factorizing the above equation,


x2 + x – 5x – 5 = 0


x(x + 1) – 5(x + 1) = 0


(x – 5) (x + 1) = 0


Solving the first part,


x – 5 = 0


x = 5


Solving the second part,


x + 1 = 0


x = -1



Question 14.

Solve the following equations by factorization method:

abx2 + (b2 – ac)x – bc = 0


Answer:

On factorizing the above equation,

abx2 + (b2 – ac)x – bc = 0


abx2 + b2x – acx – bc = 0


bx(ax + b) – c(ax + b) = 0


(bx – c) (ax + b) = 0


Solving the first part,


bx – c = 0


bx = c


x = c/b


Solving the second part,


ax + b = 0


ax = -b


x = -b / a




Exercise 3.4
Question 1.

Solve the following quadratic equations by the method of completing the square:

3x2 – 5x + 2 = 0


Answer:

Now in the above quadratic equation the coefficient of x2 is 3. Let us make it unity by dividing the entire quadratic equation by 3.

x2 – 5/3x + 2/3 = 0


x2 – 5/3x = -2/3


Now by taking half of the coefficient of x and then squaring it and adding on both LHS and RHS sides.


Coefficient of x = 5/3


Half of 5/3 = 5/6


Squaring the half of 5/3 = 25/36



Now the LHS term is a perfect square and can be expressed in the form of (a-b) 2 = a2 – 2ab + b2 where a = x and b = 5/6



On simplifying both RHS and LHS we get an equation of following form,


(x ± A)2 = k2



Taking Square root of both sides.



Now taking the positive part,




x = 6/6


x = 1


Now taking the negative part,




x = 4/6


x = 2/3



Question 2.

Solve the following quadratic equations by the method of completing the square:

5x2 – 6x – 2 = 0


Answer:

Now in the above quadratic equation the coefficient of x2 is 5. Let us make it unity by dividing the entire quadratic equation by 5.

x2 – 6/5x - 2/5 = 0


x2 – 6/5x = 2/5


Now by taking half of the coefficient of x and then squaring it and adding on both LHS and RHS sides.


Coefficient of x = 6/5


Half of 6/5 = 6/10


Squaring the half of 6/10 = 36/100



Now the LHS term is a perfect square and can be expressed in the form of (a-b) 2 = a2 – 2ab + b2 where a = x and b = 6/10



On simplifying both RHS and LHS we get an equation of following form,


(x ± A)2 = k2



Taking Square root of both sides.



Now taking the positive part,







Now taking the negative part,


Now taking the positive part,








Question 3.

Solve the following quadratic equations by the method of completing the square:

4x2 + 3x + 5 = 0


Answer:

Now in the above quadratic equation the coefficient of x2 is 4. Let us make it unity by dividing the entire quadratic equation by 4.

x2 – 3/4x + 5/4 = 0


x2 – 3/4x = -5/4


Now by taking half of the coefficient of x and then squaring it and adding on both LHS and RHS sides.


Coefficient of x = 3/4


Half of 3/4 = 3/8


Squaring the half of 3/4 = 9/64



Now the LHS term is a perfect square and can be expressed in the form of (a-b) 2 = a2 – 2ab + b2 where a = x and b = 3/8



On simplifying both RHS and LHS we get an equation of following form,


(x ± A)2 = k2



It is observed that the term obtained on RHS is a negative term and taking square root of a negative term will give imaginary roots for the given quadratic equation.


Therefore the given quadratic equation does not has real roots.



Question 4.

Solve the following quadratic equations by the method of completing the square:




Answer:

Now in the above quadratic equation the coefficient of x2 is 4. Let us make it unity by dividing the entire quadratic equation by 4.

x2 + √3x + 3/4 = 0


x2 + √3x = -3/4


Now by taking half of the coefficient of x and then squaring it and adding on both LHS and RHS sides.


Coefficient of x = √3


Half of √3= √3/2


Squaring the half of √3= 3/4



Now the LHS term is a perfect square and can be expressed in the form of (a-b) 2 = a2 – 2ab + b2 where a = x and b = √3/2



On simplifying both RHS and LHS we get an equation of following form,


(x ± A)2 = k2


Here RHS term is zero which implies that the roots of the quadratic equation are real and equal.


Taking square root of both sides,





Question 5.

Solve the following quadratic equations by the method of completing the square:

2x2 + x – 4 = 0


Answer:

Now in the above quadratic equation the coefficient of x2 is 2. Let us make it unity by dividing the entire quadratic equation by 2.

x2 + 1/2x - 2 = 0


x2 + 1/2 x = 2


Now by taking half of the coefficient of x and then squaring it and adding on both LHS and RHS sides.


Coefficient of x = 1/2


Half of 1/2 = 1/4


Squaring the half of 1/2 = 1/16



Now the LHS term is a perfect square and can be expressed in the form of (a-b) 2 = a2 – 2ab + b2 where a = x and b = 1/4



On simplifying both RHS and LHS we get an equation of following form,


(x ± A)2 = k2



Taking Square root of both sides.



Now taking the positive part,





Now taking the negative part,






Question 6.

Solve the following quadratic equations by the method of completing the square:

2x2 + x + 4 = 0


Answer:

Now in the above quadratic equation the coefficient of x2 is 2. Let us make it unity by dividing the entire quadratic equation by 2.

x2 + 1/2 x + 2= 0


x2 + 1/2 x = - 2


Now by taking half of the coefficient of x and then squaring it and adding on both LHS and RHS sides.


Coefficient of x = 1/2


Half of 1/2 = 1/4


Squaring the half of 1/2 = 1/16



Now the LHS term is a perfect square and can be expressed in the form of (a-b) 2 = a2 – 2ab + b2 where a = x and b = 1/4



On simplifying both RHS and LHS we get an equation of following form,


(x ± A)2 = k2



It is observed that the term obtained on RHS is a negative term and taking square root of a negative term will give imaginary roots for the given quadratic equation.


Therefore the given quadratic equation does not has real roots.



Question 7.

Solve the following quadratic equations by the method of completing the square:

4x2 + 4bx – (a2 – b2) = 0


Answer:

Now in the above quadratic equation the coefficient of x2 is 4. Let us make it unity by dividing the entire quadratic equation by 4.

4x2 + 4bx – (a2 – b2) = 0


x2 + bx = (a2 – b2)/4


Now by taking half of the coefficient of x and then squaring it and adding on both LHS and RHS sides.


Coefficient of x = b


Half of b = b/2


Squaring the half of b = b/4



Now the LHS term is a perfect square and can be expressed in the form of (a-b) 2 = a2 – 2ab + b2 where a = x and b = b/2




On simplifying both RHS and LHS we get an equation of following form,


(x ± A)2 = k2



Taking Square root of both sides.



Now taking the positive part,




x = (a – b) / 2


Now taking the negative part,




x = - (a + b) / 2



Question 8.

Find the root of the following quadratic equations, if they exist, by using the quadratic formula by Shridharacharya Method:




Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = 2


b = -2√2


c = 1


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (-2√2)2 – (4 × 2 × 1)


⟹ (4 × 2) - 8


⟹ 8 – 8


⟹ 0


Since b2 – 4ac = 0 the roots are real and equal.


Now let us put the values in the above formula






x = 1/√2 , 1/√2



Question 9.

Find the root of the following quadratic equations, if they exist, by using the quadratic formula by Shridharacharya Method:

9x2 + 7x – 2 = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = 9


b = 7


c = -2


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (7)2 – (4 × 9 × -2)


⟹ 49 – (-72)


⟹ 49 + 72


⟹ 121


Since b2 – 4ac = 121 the roots are real and distinct.


Now let us put the values in the above formula






Solving with positive value first,



x = 4 / 18


x = 2/9


Solving with negative value second,



x = -18 / 18


x = -1



Question 10.

Find the root of the following quadratic equations, if they exist, by using the quadratic formula by Shridharacharya Method:




Answer:

Let us solve the above equation by equating it to zero,



x2 + 1 = 3x


x2 – 3x + 1 = 0


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 1


b = -3


c = 1


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (-3)2 – (4 × 1 × 1)


⟹ 9 – 4


⟹ 5


Since b2 – 4ac = 5 the roots are real and distinct.


Now let us put the values in the above formula






Question 11.

Find the root of the following quadratic equations, if they exist, by using the quadratic formula by Shridharacharya Method:




Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = √2


b = 7


c = 5√2


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (7)2 – (4 × √2 × 5√2)


⟹ 49 – (20 × 2)


⟹ 49 – 40


⟹ 9


Since b2 – 4ac = 121 the roots are real and distinct.


Now let us put the values in the above formula






Solving with positive value first,







x = -√2


Solving with negative value second,






Question 12.

Find the root of the following quadratic equations, if they exist, by using the quadratic formula by Shridharacharya Method:

x2 + 4x + 5 = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = 1


b = 4


c = 5


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (4)2 – (4 × 1 × 5)


⟹ 16 – 20


⟹ -4


Since b2 – 4ac = -4 the roots are imaginary.


Therefore the given quadratic equation does not has real roots.



Question 13.

Find the root of the following quadratic equations, if they exist, by using the quadratic formula by Shridharacharya Method:




Answer:

Let us solve the above equation by equating it to zero,




-2 = 3(x2 – 2x)


3x2 – 6x + 2 = 0


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 3


b = -6


c = 2


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (-6)2 – (4 × 3 × 2)


⟹ 36 – 24


⟹ 12


Since b2 – 4ac = 5 the roots are real and distinct.


Now let us put the values in the above formula









Question 14.

Find two consecutive odd positive integers, sum of whose squares is 290.


Answer:

Let the two consecutive odd integers be a and a + 2.

Given:


Sum of squares of numbers = 290


(a)2 + (a + 2)2 = 290


a2 + 4a + 4 + a2 = 290


2a2 + 4a + 4 = 290


2a2 + 4a – 290 + 4= 0


2a2 + 4a – 286 =0


2(a2 + 2a – 143) =0


a2 + 2a – 143 =0


On factorizing the above equation,


a2 + 2a – 143 =0


Sum = 2


Product = 143


Therefore the two numbers satisfying the above conditions are -11 and 13.


a2 + 13a – 11a – 143 =0


a(a + 13) -11(a + 13) = 0


(a – 11) (a + 13) = 0


Solving first part,


a – 11 = 0


a = 11


Solving second part,


a + 13 = 0


a = -13


Given that the numbers are positive. So a = -13 is not possible.


So First number is 11 and consecutive positive odd number is 13.



Question 15.

The difference of squares of two numbers is 45 and the square of the smaller number is four times the larger number. Find the two numbers.


Answer:

Let larger number be x and smaller number be y.

Given:


(Large Number)2 – (Smaller Number)2 = 45


x2 – y2 = 45


y2 = x2 – 45


Also Smaller Number2, y2 = 4 × Large Number


x2 – 45 = 4x


x2 – 4x – 45 = 0


On factorizing the above equation,


Sum = -4


Product = -45


Therefore the two numbers satisfying the above conditions are -9 and 5.


x2 – 9x + 5x – 45 = 0


x(x – 9) + 5(x – 9) = 0


(x – 9) (x + 5) = 0


Solving first part,


x – 9 = 0


x = 9


Solving second part,


x + 5 = 0


x = -5


If x = 9, then


y2 = 4 × 9


y2 = 36


y =± 6


If x = -5, then


y2 = 4 × -5


y2 = -20


Value of y becomes imaginary which is not possible.


So possible values of x and y are 9, 6 or 9, -6.



Question 16.

Divide 16 into two parts such that two times the square of the larger part is 164 more than the square of the smaller part.


Answer:

Let the smaller part be x and the larger part be 16 – x.

Given:


2 × (Larger Part)2 = (Smaller Part)2 + 164


2 × (16 – x)2 = (x)2 + 164


2 × (256 – 32x + x2) = x2 + 164


512 – 64x + 2 x2 = x2 + 164


x2 – 64x + 512 – 164 = 0


x2 – 64x + 348 = 0


On factorizing the above equation,


Sum = -64


Product = 348


Therefore the two numbers satisfying the above conditions are -58 and -6.


x2 – 6x - 58x + 348 = 0


x(x – 6) - 58(x – 6) = 0


(x – 6) (x - 58) = 0


Solving first part,


x – 6 = 0


a = 6


Solving second part,


x - 58 = 0


x = 58


Since x is the smaller it cannot be greater than 16. Hence x cannot be 58


So the smaller part is x = 6


So the larger Part = 16 – 6


= 10




Exercise 3.5
Question 1.

Find the nature of the roots of the following quadratic equations:

2x2 – 3x + 5 = 0


Answer:

Nature of the quadratic equation can be found out using the following formula

b2 – 4ac > 0 for real roots


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 2


b = -3


c = 5


⟹ (-3)2 – (4 × 2 × 5)


⟹ 9 – 40


⟹ -31


The answer is negative which implies that the quadratic equation does not have real roots that is they have imaginary roots.



Question 2.

Find the nature of the roots of the following quadratic equations:

2x2 – 4x + 3 = 0


Answer:

Nature of the quadratic equation can be found out using the following formula

b2 – 4ac > 0 for real roots


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 2


b = -4


c = 3


⟹ (-4)2 – (4 × 2 × 3)


⟹ 16 – 24


⟹ -8


The answer is negative which implies that the quadratic equation does not have real roots that is they have imaginary roots.



Question 3.

Find the nature of the roots of the following quadratic equations:

2x2 + x – 1 = 0


Answer:

Nature of the quadratic equation can be found out using the following formula

b2 – 4ac > 0 for real roots


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 2


b = 1


c = -1


⟹ (1)2 – (4 × 2 × -1)


⟹ 1 – (-8)


⟹ 1 + 8


⟹ 9


The answer is positive and also a perfect square which implies that the quadratic equation has real and distinct roots.



Question 4.

Find the nature of the roots of the following quadratic equations:

x2 – 4x + 4 = 0


Answer:

Nature of the quadratic equation can be found out using the following formula

b2 – 4ac > 0 for real roots


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 1


b = -4


c = 4


⟹ (-4)2 – (4 × 1 × 4)


⟹ 16 - 16


⟹ 0


The answer is zero which implies that the quadratic equation has real and equal roots.



Question 5.

Find the nature of the roots of the following quadratic equations:

2x2 + 5x + 5 = 0


Answer:

Nature of the quadratic equation can be found out using the following formula

b2 – 4ac > 0 for real roots


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 2


b = 5


c = 5


⟹ (25)2 – (4 × 2 × 5)


⟹ 25 - 40


⟹ -15


The answer is negative which implies that the quadratic equation does not have real roots that is they have imaginary roots.



Question 6.

Find the nature of the roots of the following quadratic equations:




Answer:

Nature of the quadratic equation can be found out using the following formula

b2 – 4ac > 0 for real roots


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 3


b = -2


c = 1/3


⟹ (-2)2 – (4 × 3 × 1/3)


⟹ 4 – 4


⟹ 0


The answer is zero which implies that the quadratic equation has real and equal roots.



Question 7.

Find that value of k in the following quadratic equation whose roots are real and equal:

kx(x – 2) + 6 = 0


Answer:

Let us first solve the above equation,

kx2 – 2kx + 6 = 0


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = k


b = -2k


c = 6


Since the quadratic equations have real and equal roots,


b2 – 4ac = 0 for real and equal roots


⟹ (-2k) 2 – (4 × k × 6) = 0


⟹ 4k2 – 24k = 0


⟹ 4k(k – 6) = 0


⟹ (k – 6) = 0 or 4k = 0


⟹ k = 6 or k = 0



Question 8.

Find that value of k in the following quadratic equation whose roots are real and equal:

x2 – 2(k + 1)x + k2 = 0


Answer:

Let us first solve the above equation,

x2 – 2kx + 1x + k2 = 0


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 1


b = -2(k+1)


c = k2


Since the quadratic equations have real and equal roots,


b2 – 4ac = 0 for real and equal roots


⟹ (-2(k+1)) 2 – (4 × k2 × 1) = 0


⟹ 4(k2 + 2k + 1) – 4 k2 = 0


⟹ 4k2 + 8k + 4 – 4 k2 = 0


⟹ 8k + 4 = 0


⟹ 8k = - 4


⟹ k = - 4/8


⟹ k = - 1/2



Question 9.

Find that value of k in the following quadratic equation whose roots are real and equal:

2x2 + kx + 3 = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = 2


b = k


c = 3


Since the quadratic equations have real and equal roots,


b2 – 4ac = 0 for real and equal roots


⟹ (k) 2 – (4 × 2 × 3) = 0


⟹ k2 – 24 = 0


⟹ k2 = 24


⟹ k = √( 2 × 2 × 6)


⟹ k = ± 2√6



Question 10.

Find that value of k in the following quadratic equation whose roots are real and equal:

(k + 1)x2 – 2(k –1)x + 1 = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = k + 1


b = -2(k – 1)


c = 1


Since the quadratic equations have real and equal roots,


b2 – 4ac = 0 for real and equal roots


⟹ (-2(k – 1)) 2 – (4 × (k + 1) × 1) = 0


⟹ 4(k2 - 2k + 1) – 4k - 4 = 0


⟹ 4k2 - 8k + 4 – 4k - 4 = 0


⟹ 4k2 - 12k = 0


⟹ 4k (k – 3) = 0


⟹ (k – 3) = 0 or 4k = 0


⟹ k = 3 or k = 0



Question 11.

Find that value of k in the following quadratic equation whose roots are real and equal:

(k + 4) x2 + (k + 1) x + 1 = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = k + 4


b = k + 1


c = 1


Since the quadratic equations have real and equal roots,


b2 – 4ac = 0 for real and equal roots


⟹ (k + 1) 2 – (4 × (k + 4) × 1) = 0


⟹ k2 + 2k + 1 – 4k - 16 = 0


⟹ k2 - 2k – 15 = 0


⟹ k2 - 2k – 15 = 0


On factorizing the above equation,


Sum = -2


Product = -15


Therefore the two numbers satisfying the above conditions are 3 and -5.


k2 – 5k + 3k – 15 = 0


k(k – 5) + 3(k – 5) = 0


(k + 3) (k – 5) = 0


Solving first part,


k + 3 = 0


k = -3


Solving second part,


k – 5 = 0


k = 5



Question 12.

Find that value of k in the following quadratic equation whose roots are real and equal:

kx2 – 5x + k = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = k


b = -5


c = k


Since the quadratic equations have real and equal roots,


b2 – 4ac = 0 for real and equal roots


⟹ (-5) 2 – (4 × k × k) = 0


⟹ 25 - 4k2 = 0


⟹ 4k2 = 25


⟹ k2 = 25/4


⟹ k= ± 5/2



Question 13.

Find these values of k for which the roots of the following quadratic equations are real and distinct:

kx2 + 2x + 1 = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = k


b = 2


c = 1


Since the quadratic equations have real and distinct roots,


b2 – 4ac > 0 for real and distinct roots


⟹ (2) 2 – (4 × k × 1) > 0


⟹ 4 – 4k > 0


⟹ 4k < 4 [Dividing both sides by 4]


⟹ k < 1



Question 14.

Find these values of k for which the roots of the following quadratic equations are real and distinct:

kx2 + 6x + 1


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = k


b = 6


c = 1


Since the quadratic equations have real and distinct roots,


b2 – 4ac > 0 for real and distinct roots


⟹ (6)2 – (4 × k × 1) > 0


⟹ 36 – 4k > 0


⟹ 4k < 36 [Dividing both sides by 4]


⟹ k < 9



Question 15.

Find these values of k for which the roots of the following quadratic equations are real and distinct:

x2 – kx + 9 = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = 1


b = -k


c = 9


Since the quadratic equations have real and distinct roots,


b2 – 4ac > 0 for real and distinct roots


⟹ (-k) 2 – (4 × 9 × 1) > 0


⟹ k 2 – 36 > 0


⟹ k 2 > 36


⟹ k > ± 6


Which implies k < -6 and k > 6.



Question 16.

Find those values of k for which the roots of the equation x2 + 5kx + 16 = 0 are not real.


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = 1


b = 5k


c = 16


For the quadratic equations to have imaginary [not real] roots,


b2 – 4ac < 0 for imaginary [not real] roots


⟹ (5k) 2 – (4 × 16 × 1) > 0


⟹ 25k 2 – 64 < 0


⟹ 25k 2 < 64


⟹ k 2 < 64/25


⟹ k <± 8/5


Therefore the range of k values for roots to be imaginary are:


-8/5 < k < 8/5



Question 17.

If the roots of the quadratic equation (b – c)x2 + (c – a)x + (a – b) = 0 are real and equal then prove that 2b = a + c.


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = b – c


b = c – a


c = a – b


Since the quadratic equations have real and equal roots,


b2 – 4ac = 0 for real and equal roots


⟹ (c – a) 2 – [4 × (b – c) × (a – b)] = 0


⟹ c2 – 2ac + a2 – [4 × (ba – b2 – ca – bc)] = 0


⟹ c2 – 2ac + a2 – [4ba – 4b2 – 4ca + 4bc] = 0


⟹ c2 – 2ac + a2 – 4ba + 4b2 + 4ca - 4bc = 0


⟹ c2 + a2 – 4ba + 4b2 + 2ac - 4bc = 0


⟹ a2 + 4b2 + c2 – 4ab - 4bc + 2ac = 0


⟹ a2 + (-2b)2 + c2 + 2 × a(-2b) + 2 × (-2b)c + 2 × ac = 0


We have the following formula:


(a + b + c)2 = a2 + b2 + c2 + 2ab + 2bc + 2ac


So according to the formula


⟹ (a + (-2b) + c) 2= 0


Taking square root of both sides


⟹ a + (-2b) + c = 0


∴ 2b = a + c


Hence Proved.




Exercise 3.6
Question 1.

Find the lowest common multiple of the following expressions:

24x2yz and 27x4y2z2


Answer:

Let u = 24x2yz

and v = 27x4y2z2


Writing u and v in factorized form which is as follows:


u = 2 × 2 × 2 × 3 × x2 × y × z


= 23 × 3 × x2 × y × z


v = 3 × 3 × 3 × x4 × y2 × z2


= 33 × x4 × y2 × z2


Now selecting the common multiples from both u and v,


= 23 × 33 × x4 × y2 × z2


= 216 x4y2z2


Therefore the LCM of u and v = 216 x4y2z2



Question 2.

Find the lowest common multiple of the following expressions:

x2 – 3x + 2 and x4 + x3 – 6x2


Answer:

Let u(x) = x2 – 3x + 2

On factorizing the above equation,


Sum = -3


Product = 2


Therefore the two numbers satisfying the above conditions are -2 and -1.


u(x) = x2 – x – 2x – 2


u(x) = x(x – 1) - 2(x – 1)


u(x) = (x – 2) (x – 1)


Let v(x) = x4 + x3 – 6x2


= x2(x2 + x – 6)


Solving the quadratic part,


⟹ x2 + x – 6


⟹ x2 + 3x – 2x – 6


⟹ x(x + 3) – 2(x + 3)


⟹ (x – 2) (x + 3)


Therefore v (x) = x2 (x – 2) (x + 3)


By comparing u(x) and v(x),


LCM = x2 (x – 2) (x + 3) (x – 1)



Question 3.

Find the lowest common multiple of the following expressions:

(iii) 2x2 – 8 and x2 – 5x + 6


Answer:

Let u(x) = 2x2 – 8

On factorizing the above equation,


u(x) = 2(x2 – 4)


Let v(x) = x2 – 5x + 6


On factorizing the above equation,


Sum = -5


Product = 6


Therefore the two numbers satisfying the above conditions are -2 and -3.


v(x) = x2 – 3x – 2x + 6


v(x) = x(x – 3) - 2(x – 3)


v(x) = (x – 2) (x – 3)


By comparing u(x) and v(x),


LCM = 2(x2 – 4) (x – 3)



Question 4.

Find the lowest common multiple of the following expressions:

x2 – 1; (x2 + 1) (x + 1) and x2 + x –1


Answer:

Let u(x) = (x2 – 1) = (x + 1) (x – 1)

Let v(x) = (x2 + 1) (x + 1)


Let w(x) = x2 + x –1


By comparing u(x), v(x) and w(x),


The LCM is = (x + 1) (x – 1) (x2 + 1) (x2 + x –1)


= (x2 – 1) (x2 + 1) (x2 + x –1)


= (x4 – 1) (x2 + x –1)



Question 5.

Find the lowest common multiple of the following expressions:

18(6x4 + x3 – x2) and 45(2x6 + 3x5 + x4)


Answer:

Let u(x) = 18(6x4 + x3 – x2)

= 18 x2(6x2 + x –1)


Let us solve the inner quadratic equation,


6x2 + x –1 = 0


6x2 + x - 1 = 0


6x2 + 3x - 2x - 1 = 0


3x(2x + 1) - 1(2x + 1) = 0


(3x – 1) (2x + 1) = 0


So u(x) = 18 x2(3x – 1) (2x + 1)


Let v(x) = 45(2x6 + 3x5 + x4)


= 45 x4(2x2 + 3x + 1)


Let us solve the inner quadratic equation,


2x2 + 3x + 1 = 0


2x2 + 2x + x + 1 = 0


2x(x + 1) + 1(x + 1) = 0


(2x + 1) (x + 1) = 0


So v(x) = 45 x4(2x + 1) (x + 1)


By comparing the above equation, we get


LCM = 90 x4(2x + 1) (x + 1) (3x – 1)



Question 6.

Find the highest common factor of the following expressions:

(i) a3b4, ab5, a2b8

(ii) 16x2y2, 48x4z

(iii) x2 – 7x + 12; x2 – 10x + 21 and x2 + 2x – 15

(iv) (x + 3)2 (x – 2) and (x + 3) (x – 2)2

(v) 24(6x4 – x3 – 2x2) and 20(6x6 + 3x5 + x4)


Answer:

(i) Let u(x) = a3b4

Let v(x) = ab5


Let w(x) = a2b8


By comparing all the above equations, we get,


HCF = ab4 (Least power of a and b)


(ii) Let u(x) = 24 × x2 × y2


Let v(x) = 24 × 3 × x4 × z


By comparing all the above equations, we get,


HCF = 24 × x2


= 16 x2 (Least power of x, y and z and also common terms of u(x) and v(x))


(iii) Let u(x) = x2 – 7x + 12


= x2 – 4x – 3x + 12


= x(x – 4) – 3(x – 4)


= (x – 3) (x – 4)


Let v(x) = x2 – 10x + 21


= x2 – 7x – 3x + 21


= x(x – 7) – 3(x – 7)


= (x – 7) (x – 3)


Let w(x) = x2 + 2x – 15


= x2 + 5x – 3x – 15


= x(x + 5) – 3(x + 5)


= (x – 3) (x + 5)


By comparing all the above equations, we get,


HCF = (x + 3) [only common term from u(x), v(x) and w(x)].


(iv) Let u(x) = (x + 3)2 (x – 2)


Let v(x) = (x + 3) (x – 2)2


By comparing all the above equations, we get,


HCF = (x + 3) (x – 2) [Least power and common term from u(x) and v(x)].


(v) Let u(x) = (8 × 3) (6x4 – x3 – 2x2)


= (8 × 3) x2 (6x2 – x – 2)


= (8 × 3) x2 (6x2 – 4x + 3x – 2)


= (8 × 3) x2 (2x (3x – 2) + 1(3x – 2))


= (8 × 3) x2 (2x + 1) (3x – 2)


Let v(x) = 20(6x6 + 3x5 + x4)


= (4 × 5) x4(6x2 + 3x + 1)


= (4 × 5) x4(6x2 + 3x + 1)


By comparing all the above equations, we get,


HCF = 4 x2 (2x + 1) [Least power and common term from u(x) and v(x)].



Question 7.

If u(x) = (x – 1)2 and v(x) = (x2 – 1) the check the true of the relation LCM × HCF = u(x) × v(x).


Answer:

u(x) = (x – 1)2

= (x – 1) (x – 1)


v(x) = (x2 – 1)


= (x + 1) (x – 1)


LCM of u(x) and v(x) = (x – 1)2 (x + 1)


HCF of u(x) and v(x) = (x – 1)


u(x) × v(x) = (x – 1) (x – 1) × (x2 – 1)


= (x2 – 2x + 1) × (x2 – 1)


= x4 – 2x3 + x2 - x2 + 2x – 1


= x4 – 2x3 + 2x – 1


HCF × LCM = (x – 1)2 (x + 1) × (x – 1)


= (x2 – 2x + 1) (x2 – 1)


= x4 – 2x3 + x2 - x2 + 2x – 1


= x4 – 2x3 + 2x – 1


So it is observed that HCF × LCM = u(x) × v(x).


Hence Proved.



Question 8.

The product of two expressions is (x – 7) (x2 + 8x + 12). If the HCF of these expressions is (x + 6) then find their LCM.


Answer:

Product = (x – 7) (x2 + 8x + 12)

= x3 + 8x2 + 12x – 7x2 – 56x – 84


= x3 + x2 – 44x - 84


The LCM = Product / HCF


= (x3 + x2 – 44x - 84) / (x + 6)


The division is as follows:




Question 9.

The HCF and LCM of two quadratic expressions are respectively (x – 5) and x3 – 19x – 30, then find both the expressions.


Answer:

HCF = (x – 5)

LCM = x3 – 19x – 30


= x3 – 19x – 38 + 8


= x3 + 8 – 19x – 38


= x3 + 23 – 19(x + 2)


x3 + 23 = (x + 2) (x2 – 2x + 4) [Using a3 + b3 = (a + b) (a2 – ab + b2)]


= (x + 2) (x2 – 2x + 4) – 19(x + 2)


= (x + 2) (x2 – 2x + 4 – 19)


= (x + 2) (x2 – 2x – 15)


= (x + 2) (x2 – 5x + 3x – 15)


= (x + 2) (x(x– 5) + 3(x – 5))


= (x + 2) (x – 5) (x + 3)


Since HCF = x – 5 it will belong to both polynomials.


So u(x) = (x – 5) (x + 3)


= x2 – 2x - 15


So v(x) = (x – 5) (x + 2)


= x2 – 3x - 10




Miscellaneous Exercise 3
Question 1.

If one zero of the polynomial f(x) = 5x2 + 13x + k is reciprocal of the other than the value of k will be:
A. 0

B. 1/5

C. 5

D. 6


Answer:

Let the first root be a.

So the second root as per the question is 1/a.


Product of zeroes = a × 1/a


= 1


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 5, b = 13, c = k


Product of zeroes = c / a


k/5 = 1


Therefore k = 5


So the correct answer is C [5].


Question 2.

The zeroes of the polynomials x2 – x – 6 are:
A. 1, 6

B. 2, –3

C. 3, –2

D. 1, –6


Answer:

Solving the quadratic part,

⟹ x2 - x – 6 = 0


⟹ x2 - 3x + 2x – 6 = 0


⟹ x(x - 3) + 2(x - 3) = 0


⟹ (x + 2) (x - 3) = 0


Solving first part,


x + 2 = 0


x = - 2


Solving second part,


x - 3 = 0


x = 3


So the correct answer is C [3, -2].


Question 3.

If one zero of the polynomial 2x2 + x + k is 3 then the value of k will be:
A. 12

B. 21

C. 24

D. –21


Answer:

Given one zero = 3

Let second zero a.


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 2, b = 1, c = k


Sum of zeroes = -b/a


3 + a = -1/2


a = -1/2 – 3


a = -7/2


Product of zeroes = 3 × (-7/2)


= -21/2


Product of zeroes = c/a


k/2 = -21/2


k = -21


So the correct answer is D [-21].


Question 4.

If α, β, are the zeroes of the polynomial x2 – p(x + 1) – c such that (α + 1) (β + 1) = 0 then the value of c will be:
A. 0

B. –1

C. 1

D. 2


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


∴ a = 1


b = -p


c = -p-c


Sum of zeroes = -b/a


= - (-p) / 1


α + β = p …………………………... (i)


Product of Zeroes = c/a


αβ = - (p + c) …………………… (ii)


Now from LHS we have,


(α + 1)(β + 1) = αβ + α + β + 1


From (i) and (ii) we have the values of αβ and (α + β)


(α + 1)(β + 1) = - (p + c) + p + 1


= - p – c + p + 1


= c + 1


Given (α + 1) (β + 1) = 0


c + 1 = 0


c = -1


So the correct answer is B [-1].


Question 5.

If the roots of the quadratic equation x2 – kx + 4 = 0 are equal then the value of k will be:
A. 2

B. 1

C. 4

D. 3


Answer:

x2 – kx + 4 = 0

When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


a = 1


b = -k


c = 4


Since the quadratic equations have real and equal roots,


b2 – 4ac = 0 for real and equal roots


⟹ (-k) 2 – (4 × 1 × 4) = 0


⟹ k2 – 16 = 0


⟹ k2 = 16


⟹ k= ± 4


So the correct answer is C [4].


Question 6.

If x = 1 is a common root of the equations ax2 + ax + 3 = 0 and x2 + x + b = 0 then the value of ab will be:
A. 1

B. 3.5

C. 6

D. 3


Answer:

Put x = 1 in the first equation,

a + a + 3 = 0


2a = -3


a = -3/2


Put x = 1 in the second equation,


1 + 1 + b = 0


b + 2 = 0


b = -2


Therefore the value of ab = -3/2 × -2


= 3


So the correct answer is D [3].


Question 7.

The discriminant of the quadratic equation will be:
A. 10

B. 64

C. 46

D. 30


Answer:

The discriminant of the equation can be found out using the following formula:

⟹ b2 – 4ac


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 3√3


b = 10


c = √3


⟹ b2 – 4ac


⟹ (10)2 – (4 × 3√3 × √3)


⟹ (10)2 – (4 × 9)


⟹ 100 – 36


= 64


So the correct answer is B [64].


Question 8.

The nature of roots of the quadratic equation 4x2 – 12x – 9 = 0 is :
A. real and equal

B. real and distinct

C. imaginary and equal

D. imaginary and distinct


Answer:

The nature of roots of the equation can be found out using the following formula:

⟹ b2 – 4ac


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 4


b = -12


c = -9


⟹ b2 – 4ac


⟹ (-12)2 – (4 × -9 × 4)


⟹ 144 – (-144)


⟹ 144 + 144


= 288


Since b2 – 4ac>0, the roots will be real and distinct.


So the correct answer is B [real and distinct].


Question 9.

The HCF of expression 8a2b2c and 20ab3c2 is:
A. 4ab2c

B. 4abc

C. 40a2b3c2

D. 40abc


Answer:

Let us write both the expressions in factorized form.

Let u(x) = 23 × a2× b2 × c


Let v(x) = 22 × 5 × a × b3 × c2


So by comparing u(x) and v(x), HCF = 4ab2c [Least power of variables and common terms]


So the correct answer is A [4ab2c].


Question 10.

The LCM of expressions x2 – 1 and x2 +2x + 1 is :
A. x + 1

B. (x2 – 1)(x + 1)

C. (x – 1)(x + 1)2

D. (x2 – 1)(x + 1)2


Answer:

Let us factorize x2 +2x + 1

But x2 +2x + 1 is a perfect square and it can be expressed as (x + 1)2


u(x) = x2 +2x + 1


u(x) = x2 +x + x + 1


u(x) = x(x + 1) +1(x + 1)


u(x) = (x + 1) (x + 1)


Let v(x) = x2 – 1


= (x + 1) (x – 1)


So by comparing both polynomials, LCM is = (x1) (x+1)2


So the correct answer is C [(x – 1)(x + 1)2].


Question 11.

If LCM of expressions 6x2y4 and 10xy2 is 30x2y4 then HCF will be:
A. 6x2y2

B. 2xy2

C. 10x2y4

D. 60x3y6


Answer:

Let u(x) = 2 × 3 × x2 × y4

Let v(x) = 2 × 5 x × x × y2


So by comparing u(x) and v(x), HCF = 2xy2 [Least power of variables and common terms]


So the correct answer is B [2xy2].


Question 12.

Write Shridharacharya Formula of finding the roots of the quadratic equation ax2 + bx + c = 0.


Answer:

The generalized formula for the quadratic equation is as follows:

ax2 + bx + c = 0


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:




Question 13.

Writing the general form of the discriminant of the equation ax2 + by + c = 0 explain the nature of the roots.


Answer:

The generalized formula for the quadratic equation is as follows:

ax2 + bx + c = 0


The discriminant of the equation can be found out using the following formula:


⟹ b2 – 4ac


If b2 – 4ac > 0, then the roots will be real and distinct.


If b2 – 4ac = 0, then the roots will be real and equal.


If b2 – 4ac < 0, then the roots will be imaginary.



Question 14.

Find the zeroes of the quadratic polynomial 2x2 – 8x + 6 and examine the truth of the relationship between the zeroes and the coefficients.


Answer:

To find the zeros of the polynomial let us first solve the polynomial by equating it to zero. Factorizing the given polynomial

2x2 – 8x + 6 = 0


To factorize the polynomial we have,


Sum of the value should be equal = -8


Product should be equal to = 2 × 6


= 12


So two numbers are -2, -6


2x2 – 2x – 6x + 6 = 0


2x(x – 1) – 6(x – 1) = 0


(2x-6)(x – 1) = 0


2x-6 = 0 or x-1 = 0


Solving first part,


2x-6 = 0


2x = 6


x = 3


Solving second part,


x – 1 = 0


x = 1


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = 2, b = -8, c = 6


Sum of zeroes = -b / a


= - (-8) / 2


= 4


Product of zeroes = c / a


= 6 / 2


= 3


Zeroes obtained are 3 and 1 and their sum is 4 and product is 3 which is matching to the answer obtained through the ratio of coefficients.



Question 15.

If α and β are the zeroes of the quadratic polynomial f(x) = x2 – px + q then find the values of the following:

(i) α2 + β2 (ii)


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


∴ a = 1


b = -p


c = q


Sum of zeroes = -b / a


= - (-p) / 1


α + β = p


Product of zeroes = c / a


= q / 1


αβ = q


(i) α2 + β2


(α + β) 2 = α2 + β2 + 2αβ


α2 + β2 = (α + β) 2 - 2αβ


= (p) 2 – 2q


= p2 – 2q


(ii)





Question 16.

If the polynomial x4– 6x3 + 16x + 10 is divided by another polynomial x2 – 2x + k and the remainder obtained is (x + a), then find the values of k and a.


Answer:

The division is as follows:


There is an important relation between dividend, divisor, quotient and remainder which is as follows:


Dividend = Divisor × Quotient + Remainder


Dividend – Remainder = Divisor as the when remainder is subtracted from dividend, the result obtained is completely divisible by divisor.


(-9 + 2k) x + (10 – 8k + k2) = (x + a)


On comparing both sides of coefficients of x:


2k – 9 = 1


2k = 10


k = 5


On comparing both sides:


10 – 8k + k2 = a


10 - (8 × 5) + 52 = a


10 – 40 + 25 = a


35 – 40 = a


-5 = a


Hence a = -5 and k = 5.



Question 17.

The area of a rectangular plot is 528 m2. The length of the plot (in m) is 1 more than double of breadth. Representing by the required quadratic equation find the length and breadth of the plot.


Answer:

Let the length be l and breadth be b.

Area = l × b


Given Length = 2b + 1


(2b + 1) × b = 528


2b2 + b = 528


2b2 + b – 528 = 0


2b2 + 33b – 32b – 528 = 0


2b(b – 16) + 33(b – 16) = 0


(2b + 33) (b – 16) = 0


Solving the first part,


2b + 33 = 0


2b = -33


b = -33/2


Solving second part,


b – 16 = 0


b = 16


Breadth cannot be negative.


So breadth = 16 m


Length = 2 × 16 + 1


= 33 m



Question 18.

Solve the quadratic equation x2 + 4x – 5 = 0 by the method of completing the square.


Answer:

x2 + 4x – 5 = 0

x2 + 4x = 5


Now by taking half of the coefficient of x and then squaring it and adding on both LHS and RHS sides.


Coefficient of x = 4


Half of 4 = 2


Squaring the half of 4 = 4


x2 + 4x + 4= 5 + 4


(x + 2)2 = 9


On simplifying both RHS and LHS we get an equation of following form,


(x ± A)2 = k2


Taking square root of both sides,


(x + 2) = ±3


Solving first with positive sign of 3,


x + 2 = 3


x = 3 – 2


x = 1


Solving with negative sign of 3,


x + 2 = -3


x = -3 – 2


x = -5



Question 19.

Solve the following equation by factorization method:




Answer:

Let us solve the above equation by equating it to zero,




-2 = 3(x2 – 2x)


3x2 – 6x + 2 = 0


These problems cannot be solved by normal factorization as it do not contain normal factors.


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (-6)2 – (4 × 3 × 2)


⟹ 36 – 24


⟹ 12


Since b2 – 4ac = 12 the roots are real and distinct.


Now let us put the values in the above formula








Question 20.

Solve the following equation by factorization method:




Answer:





Cross multiplying,


7× 6 = 6 × (x2 – 4x - 5)


42 = 6x2 – 24x – 30


6x2 – 24x – -30 - 42= 0


6x2 – 24x – 72= 0


6(x2 – 4x – 12) = 0


x2 – 4x – 12 = 0


On factorizing,


x2 – 6x + 2x – 12 = 0


x(x – 6) + 2(x – 6) = 0


(x + 2) (x – 6) = 0


Solving first part,


x + 2 = 0


x = -2


Solving second part,


x – 6 = 0


x = 6



Question 21.

Solve the following equation by factorization method:




Answer:

Let us solve the above equation by equating it to zero,



x2 - 1 = 3x


x2 – 3x - 1 = 0


These problems cannot be solved by normal factorization as it do not contain normal factors.


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (-3)2 – (4 × 1 × -1)


⟹ 9 + 4


⟹ 13


Since b2 – 4ac = 13 the roots are real and distinct.


Now let us put the values in the above formula






Question 22.

Solve the following equation by factorization method:




Answer:





Cross Multiplying,


30 × (-11) = 11 × (x2 – 3x - 28)


-330 = 11x2 – 33x – 308


11x2 – 33x – 308 + 330 = 0


11x2 – 33x + 22 = 0


11(x2 – 3x + 2) = 0


x2 – 3x + 2 = 0


On factorizing,


x2 – 2x – x + 2 = 0


x (x – 2) –1(x – 2) = 0


(x – 2) (x – 1) = 0


Solving first part,


x – 2 = 0


x = 2


Solving Second part,


x – 1 = 0


x = 1



Question 23.

If one root of a quadratic equation 2x2 + px – 15 = 0 is –5 and the root of the quadratic equation p(x2 + x) + k = 0 are equal then find the value of k.


Answer:

Since -5 is the zero of the first equation,

Put x = -5 in first equation


2(-5)2 + p (-5) – 15 = 0


2× 25 – 5p – 15 = 0


5p = 50 – 15


5p = 35


p = 7


If the roots are equal, then


b2 – 4ac = 0


When we compare the above quadratic equation with the generalized one we get,


ax2 + bx + c = 0


∴ a = p = 7


b = p = 7


c = k


(7)2 – (4 × 7 × k) = 0


(7)2 – 28 k = 0


28k = 49


k = 49 / 28


k = 7 / 4



Question 24.

Solve the following quadratic equations by using Shridharacharya Quadratic Formula:

p2x2 + (p2 – q2)x – q2 = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = p2


b = (p2 – q2)


c = – q2


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ ((p2 – q2)) 2 – (4 × p × – q2)


⟹ (p4 –2 p2 q2 + q4) - (-4p2q2)


⟹ p4 –2 p2 q2 + q4 + 4p2q2


⟹ (p4 + 2 p2 q2 + q4)


⟹ ((p2 + q2)) 2


Now let us put the values in the above formula




Solving with positive value first,




x = q2 / p2


Solving with negative value second,




x = -1



Question 25.

Solve the following quadratic equations by using Shridharacharya Quadratic Formula:

9x2 – 9(a + b)x + (2a2 + 5ab + 2b2) = 0


Answer:

When we compare the above quadratic equation with the generalized one we get,

ax2 + bx + c = 0


a = 9


b = – 9(a + b)


c = (2a2 + 5ab + 2b2)


There is one formula developed by Shridharacharya to determine the roots of a quadratic equation which is as follows:



Before putting the values in the formula let us check the nature of roots by b2 – 4ac >0


⟹ (– 9(a + b)) 2 – (4 × 9 × (2a2 + 5ab + 2b2))


⟹ 81(a2 +2ab + b2) - (36(2a2 + 5ab + 2b2))


⟹ 81a2 +162ab + 81b2 - 72a2 - 180ab - 72b2


⟹ 9a2 - 18ab + 9b2


⟹ 9(a2 - 2ab + b2)


⟹ 32(a – b) 2


Now let us put the values in the above formula




Solving with positive value first,






Solving with negative value second,







Question 26.

The LCM and HCF of two quadratic expressions are respectively x3 – 7x + 6 and (x – 1). Find the expressions.


Answer:

Given:

HCF = x – 1


Let the two polynomials be u(x) and v(x)


So (x – 1) is common to both u(x) and v(x)


LCM = x3 – 7x + 6


= x3 – 7x + 6


= x3 – (1 + 6) x + 6


= x3 – x - 6x + 6


= x(x2 – 1) - 6(x - 1)


(x2 – 1) = (x + 1) (x – 1)


a2 – b2 = (a + b) (a – b)


Here a = x and b = 1


= x(x + 1) (x – 1) - 6(x - 1)


= (x-1) [x(x + 1) - 6]


Now solving the inner quadratic equation,


x2 + x - 6 = 0


x2 + 3x - 2x - 6 = 0


x(x + 3) - 2(x + 3) = 0


(x + 3) (x – 2) = 0


∴ LCM = (x-1) (x + 3) (x – 2)


Since HCF = (x-1), which implies that both u(x) and v(x) contains (x – 1)


Therefore u(x) = (x – 1) (x + 3)


= x2 + 2x - 3


v (x) = (x – 1) (x – 2)


= x2 – 3x + 2


Therefore the polynomial are x2 + 2x – 3 and x2 – 3x + 2.



Question 27.

The LCM of two polynomials in x3 – 6x2 + 3x + 10 and HCF is (x + 1). If one polynomial is x2 – 4x – 5 then find the other polynomial.


Answer:

LCM = x3 – 6x2 + 3x + 10

= x3 – 5x2 - x2 + 3x + 10


= x2(x – 5) – (x2 – 3x – 10)


= x2(x – 5) – (x2 – 5x + 2x – 10)


= x2(x – 5) – (x(x – 5) + 2(x – 5))


= x2(x – 5) – (x + 2) (x – 5)


= (x – 5) [x2 – x -2]


= (x – 5) [x2 – 2x + x -2]


= (x – 5) [x(x – 2) +1(x – 2)]


= (x – 5) (x – 2) (x + 1)


Since HCF = (x + 1) it belongs to both the polynomials.


So u(x) = (x + 1) (x – 5)


= x2 – 4x - 5


So v(x) = (x + 1) (x – 2)


= x2 – x - 2