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

$\arcsin \left(- 1\right) = - 90 + 360 k , k \in \mathbb{Z}$
If we set $x = \arcsin \left(- 1\right)$, then $\sin x = - 1$
This is easy to solve as we know a sinusoidal wave touches $y = - 1$ at $- 90 , 270 , 630$ etc.