Answer
$\Rightarrow \sin ^{-1}\left( \sin \dfrac {\pi }{4}\right) =\dfrac {\pi }{4}$
Work Step by Step
$\sin ^{-1}\left( \sin x\right) =x\left( -\dfrac {\pi }{2}\leq x\leq \dfrac {\pi }{2}\right) $
$\Rightarrow \sin ^{-1}\left( \sin \dfrac {\pi }{4}\right) =\dfrac {\pi }{4}$