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