Question

If $f(x)=|\cos x|$ then $f^1\left(\frac{\pi }{4}\right)$ is

• A. $\frac{1}{\sqrt{2}}$
• B. $\frac{-1}{\sqrt{2}}$
• C. 0
• D. Not exist

Answer 1

Answer: (B)

$f(x)=|\cos x|=\cos x$,
if $0<x<\frac{\pi }{2}$
$f^1(x)=-\sin x$
$f^1\left(\frac{\pi }{4}\right)=\frac{-1}{\sqrt{2}}$