MCQ
$2 x^3-6 x+5$ is an increasing function, if
  • A
    $0 < x < 1$
  • B
    $-1 < x < 1$
  • $x < -1$ or $x > 1$
  • D
    $-1 < x < -\frac{1}{2}$

Answer

Correct option: C.
$x < -1$ or $x > 1$
Let $f(x)=2 x^3-6 x+5$
On differentiating $\ce{w.r.t. x}$, we get $f^{\prime}(x)=6 x^2-6$
Since, it is increasing function.
$\Rightarrow 6 x^2-6>0 $
$\Rightarrow(x-1)(x+1)>0$
$\Rightarrow x >1 \text { or } x<-1$

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