Answer
$\pi$
Work Step by Step
$y = \cos^{-1}{x} \hspace{15pt} \to \hspace{15pt} x = \cos{y}$
$\text{where } \hspace{15pt} -1 \leq x \leq 1 \hspace{15pt} \text{and} \hspace{15pt} 0 \leq y \leq \pi$
Let $\theta = \cos^{-1} {(-1)} \hspace{20pt} 0 \leq \theta \leq \pi$
Since $\theta = \cos^{-1} {(-1)}$, then
$\cos{\theta} = -1$
Referring to Table 2 on page 469:
The only angle in the interval $\left[0,\pi \right]$ whose cosine is $-1$ is $\pi$.
Therefore, $\cos^{-1} {(-1)} =\pi$.
