CA Foundation Exam  >  CA Foundation Questions  >  If the sum of the roots of quadratic equation... Start Learning for Free
 If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation is
  • a)
    x2 – 3x + 1 = 0
  • b)
    3x2 -9x+27 = 0
  • c)
    9x2 – 27x + 20 = 0
  • d)
    9x2 – 27x + 10 = 0
Correct answer is option 'C'. Can you explain this answer?
Most Upvoted Answer
If the sum of the roots of quadratic equation is ‘3’ and t...
Solution:

Given that the sum of the roots of the quadratic equation is 3 and the sum of the cubes of the roots is 7.

Let the roots of the quadratic equation be α and β.

According to the problem,

α + β = 3

α3 + β3 = 7

We know that,

α3 + β3 = (α + β) (α2 - αβ + β2)

Substituting the values from the given equations,

7 = 3 (α2 - αβ + β2)

α2 - αβ + β2 = 7/3

Now, we also know that the sum of the roots of the quadratic equation is given by

α + β = -b/a

where a and b are the coefficients of x2 and x in the quadratic equation.

Substituting the values from the given equation,

α + β = -(-b/a) = b/a

b/a = 3

b = 3a

We need to find the quadratic equation. Let the quadratic equation be

ax2 + bx + c = 0

We know that the sum of the roots of the quadratic equation is given by

α + β = -b/a

Substituting the values of b and a, we get

α + β = -3a/a = -3

α + β + 3 = 0

We also know that the sum of the product of the roots taken two at a time is given by

αβ = c/a

Substituting the values of a and b, we get

αβ = c/a = 1/3

αβ - c/a = 0

Multiplying both sides by 3a, we get

3αβ - 3c = 0

αβ = c/3

Substituting the values of αβ and α + β in the equation α2 - αβ + β2 = 7/3, we get

α2 - (c/3) + β2 = 7/3

Multiplying both sides by 3, we get

3α2 - c + 3β2 = 7

We also know that

α2 + β2 = (α + β)2 - 2αβ

Substituting the values of α + β and αβ, we get

α2 + β2 = 32 - 2(c/3)

3α2 + 3β2 = 9 - 2c

Adding this equation to the equation 3α2 - c + 3β2 = 7, we get

6α2 + 6β2 - c = 16

Substituting the value of c in this equation, we get

6α2 + 6β2 - (αβ) = 16/3

Multiplying both sides by 3, we get

18α2 + 18β2 - αβ = 16

Substituting the values of αβ and α + β in the equation α2 - αβ + β2 = 7/3, we get

6α2 + 6β2 - (α2 + β2 - (7/3)) = 16

5α2 + 5β2 = 31/3

Multiplying both sides by 3, we get

Explore Courses for CA Foundation exam
If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer?
Question Description
If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer? for CA Foundation 2024 is part of CA Foundation preparation. The Question and answers have been prepared according to the CA Foundation exam syllabus. Information about If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer? covers all topics & solutions for CA Foundation 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer?.
Solutions for If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer? in English & in Hindi are available as part of our courses for CA Foundation. Download more important topics, notes, lectures and mock test series for CA Foundation Exam by signing up for free.
Here you can find the meaning of If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer? defined & explained in the simplest way possible. Besides giving the explanation of If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer?, a detailed solution for If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer? has been provided alongside types of If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer? theory, EduRev gives you an ample number of questions to practice If the sum of the roots of quadratic equation is ‘3’ and the sum of the cubes of the roots is ‘7’ then the equation isa)x2– 3x + 1 = 0b)3x2-9x+27 = 0c)9x2– 27x + 20 = 0d)9x2– 27x + 10 = 0Correct answer is option 'C'. Can you explain this answer? tests, examples and also practice CA Foundation tests.
Explore Courses for CA Foundation exam

Top Courses for CA Foundation

Explore Courses
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev