# How do you calculate the cos^-1 (-sqrt2/2)?

Evaluate ${\cos}^{-} 1 \left(- \frac{\sqrt{2}}{2}\right)$
Ans:$\pm \frac{3 \pi}{4}$
$\cos x = - \frac{\sqrt{2}}{2}$ --> arc $x = \pm \frac{3 \pi}{4}$