## Thomas' Calculus 13th Edition

$\arctan (-\dfrac{\pi}{4})$
Here, we have $\lim\limits_{(x,y,z) \to (\frac{-1}{4},\frac{\pi}{2}, 2)} \tan^{-1} (xyz)=\tan^{-1} [(\dfrac{-1}{4})(\dfrac{\pi}{2})(2)]$ Plug the limits $\tan^{-1}(-\dfrac{\pi}{4})=\arctan (-\dfrac{\pi}{4})$