Practicing Success

Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Algebra

Question:

If $(x+y)^3-(x-y)^3-3 y\left(2 x^2-3 y^2\right)=k y^3$, then find the value of k.

Options:

10.5

8

11

10

Correct Answer:

11

Explanation:

If $(x+y)^3-(x-y)^3-3 y\left(2 x^2-3 y^2\right)=k y^3$

k = ?

(a + b)3 = a3 + b3 + 3ab (a + b)

(a - b)3  = a3 - b3 - 3ab (a - b)

 (x + y)3 - (x - y)3 - 3y(2x2 - 3y2) = ky3

= x3 + y3 + 3x2y + 3xy2 - x3 + y3 + 3x2y - 3xy2 - 6yx+ 9y3 = ky3

= 11y3 = ky3

= k = 11