Answer
$-\dfrac{\pi}{4}$
Work Step by Step
We need to find the limit for $\lim\limits_{(x,y,z) \to (1,-1,-1)} \tan^{-1} (x+y+z)$
or, $\tan^{-1} (1-1-1)=\tan^{-1} (-1)$
Thus, $-\tan^{-1} (\tan (\pi/4))=-\dfrac{\pi}{4}$
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