MCQ
$f(x) = {x^3} - 27x + 5$ is an increasing function, when
  • A
    $x < - 3$
  • $|x|\, > 3$
  • C
    $x \le - 3$
  • D
    $|x|\, < 3$

Answer

Correct option: B.
$|x|\, > 3$
b
(b) To be increasing $f'(x) = 3{x^2} - 27 > 0$

$ \Rightarrow {x^2} > 9$==> $|x| > 3$.

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