Chapter 7 - Trigonometric Identities and Equations - 7.5 Inverse Circular Functions - 7.5 Exercises - Page 708: 16

$\displaystyle \frac{\pi}{2}$

$y=\cos^{-1}x =\arccos x$ Domain:$[-1, 1] $ Range: $[0, \pi]$ ----------- $y$ is the number from $[0, \pi]$ such that $\cos y=0$ $\displaystyle \cos\frac{\pi}{2}=0,\quad$and $\displaystyle \frac{\pi}{2}\in [0, \pi]$, so $\displaystyle \arccos(0)=\frac{\pi}{2}$