## Precalculus: Mathematics for Calculus, 7th Edition

$\frac{\pi}{4}$
$\tan^{-1}(\tan(\frac{\pi}{4}))= \tan^{-1}(1)$ Let $\tan^{-1}(1)=y$. Then, $\tan y= 1= \tan\frac{\pi}{4}$ $⇒y=\frac{\pi}{4}$