# How do you find the exact value of cos^-1(-1)?

Jan 28, 2018

$\left(2 n \pm 1\right) \pi$ where $n \in \mathbb{Z}$

#### Explanation:

Assume,
$\implies {\cos}^{-} 1 \left(- 1\right) = \theta$
$\implies \cos \theta = - 1$
$\implies \cos \theta = \cos \pi$
$\implies \theta = 2 n \pi \pm \pi$ where, $n \in \mathbb{Z}$
$\implies \theta = \left(2 n \pm 1\right) \pi$ ; $n \in \mathbb{Z}$