The function x^4 - 4x is decreasing in the interval - Vidyadip

MCQ

The function ${x^4} - 4x$ is decreasing in the interval

A
$[-1, 1]$
✓
$( - \infty ,\,\,1)$
C
$[1,\,\, + \infty )$
D
None of these

✓

Answer

Correct option: B.

$( - \infty ,\,\,1)$

b
(b) Let $f(x) = {x^4} - 4x \Rightarrow f'(x) = 4{x^3} - 4$

So, $4{x^3} - 4 < 0$ or ${x^3} < 1$

Hence function of decreasing in $( - \infty ,1)$.

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