Answer
$y=-\frac{\pi}{3}$
Work Step by Step
RECALL:
$y=\tan^{-1}{x} \longrightarrow \tan{y}=x$
Note that $\tan {(\frac{\pi}{3})}=\sqrt3$.
Since tangent is an odd function, $\tan{(-x)}=-\tan{x}$.
Thus, $\tan{(-\frac{\pi}{3})}=-\tan{(\frac{\pi}{3})}=-\sqrt3$
Therefore,
$y=\tan^{-1}{(-\sqrt3)}\longrightarrow y=-\frac{\pi}{3}$