Target Exam

CUET

Subject

-- Mathematics - Section A

Chapter

Applications of Derivatives

Question:

At what value of x is the function y = \( { x }^{ 3 } -36x\) attains its extreme values?

Options:

$2\sqrt { 3 }$

$-2\sqrt { 3 }$

Both \(3\sqrt { 2 }\) and \(-3\sqrt { 2 }\)

Neither \(2\sqrt { 3 }\) nor \(-2\sqrt { 3 }\)

Correct Answer:

Both \(3\sqrt { 2 }\) and \(-3\sqrt { 2 }\)

Explanation:

The correct answer is Option (3) → Both \(3\sqrt { 2 }\) and \(-3\sqrt { 2 }\)

$f(x)=x^3-36x$

and, for critical points $f'(c)=0$

$⇒3x^2-12=0$

$⇒x^2=12$

$⇒x=±\sqrt{12}=3\sqrt{2}\,or\,-3\sqrt{2}$