Question

Find the stationary points of $f\left(x\right)=\cos x$ where $0<x<2\pi$

Answer 1

$f\left(x\right)=\cos x{f}^{\prime }\left(x\right)=-\sin x$

For Stationary points $f^{\prime }\left(x\right)=0$

$-\sin x=0$

$x=0,\pi$