Answer
$0$
Work Step by Step
$y=\tan^{-1} x =\arctan x$
Domain: $(-\infty, \infty) $
Range: $(-\displaystyle \frac{\pi}{2}, \displaystyle \frac{\pi}{2})$
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$y$ is the number from $(-\displaystyle \frac{\pi}{2}, \displaystyle \frac{\pi}{2})$ such that $\tan y=$0
$\tan(0)=0\qquad$and$\displaystyle \quad 0\in(-\frac{\pi}{2}, \displaystyle \frac{\pi}{2})$,
so
$\tan^{-1} (0) =0$