Practicing Success

Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Algebra

Question:

If $x = \sqrt[3]{5} + 2 $, then the value of $x^3 = 6x^2 + 12 x- 12$ is equal to:

Options:

0

2

1

-1

Correct Answer:

1

Explanation:

(a - b)3 = a3 - b3 - 3ab(a-b)

If $x = \sqrt[3]{5} + 2 $,

then the value of $x^3 = 6x^2 + 12 x- 12$

If $x = \sqrt[3]{5} + 2 $

= x - 2 = $ \sqrt[3]{5}$

= (x - 2)3 = 5

 x3 - 6x2 + 12x - 8 = 5

⇒ x3 - 6x2 + 12x - 13 = 0 

⇒ x3 - 6x2 + 12x - 13 + 1 = 1

⇒ x3 - 6x2 + 12x - 12 = 1