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

$- \frac{\pi}{4}$
Begin with the 'inside function'. That is $\cos \left(\pi\right)$
now $\cos \left(\pi\right) = - 1$
$\Rightarrow {\tan}^{-} 1 \left(- 1\right) = - \frac{\pi}{4}$