Question:
$f(x)=\cos x, 0
Solution:
Given : $f(x)=\cos x$
$\Rightarrow f^{\prime}(x)=-\sin x$
For a local maximum or a local minimum, we must have
$f^{\prime}(x)=0$
$\Rightarrow-\sin x=0$
$\Rightarrow \sin x=0$
$\Rightarrow x=0$ or $\pi$
Since $0
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