f(x) = x^3 - 27x + 5 is an increasing function, when - Vidyadip

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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