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CUET · MATHS · PYQ PAPER 2023

The function \(f(x)=x^3-3 x\) is :

  1. A Increasing in \((0, \infty)\) and decreasing in \((-\infty, 0)\)
  2. B Decreasing in \((0, \infty)\) and increasing in \((-\infty, 0)\)
  3. C Decreasing in \((-\infty,-1] \cup[1, \infty)\) and increasing in \((-1,1)\)
  4. D Increasing in \((-\infty,-1] \cup[1, \infty)\) and decreasing in \((-1,1)\)
Verified Solution

Answer & Solution

Correct Answer

(D) Increasing in \((-\infty,-1] \cup[1, \infty)\) and decreasing in \((-1,1)\)

Step-by-step Solution

Detailed explanation

\(f'(x) = 3x^2 - 3\) \(3x^2 - 3 = 0 \implies x^2 = 1 \implies x = \pm 1\) \(f'(x) > 0\) for \(x \in (-\infty, -1) \cup (1, \infty)\) \(f'(x) Increasing in \((-\infty,-1] \cup[1, \infty)\) and decreasing in \((-1,1)\)