How would I evaluate the following trigonometric expression?

Question

$\csc^{-1}\left({-2\sqrt3 \over 3}\right)$

I've tried using a calculator, but it only shows "math error." I don't know how to process it by hand. The answer is $-60°$.

Answer 1

$$\begin{align} \csc^{-1}\left({-2\sqrt3 \over 3}\right)&=-\csc^{-1}\left({2 \over \sqrt3}\right)\\ &=-\sin^{-1}{\sqrt3\over2}\\ &=-{\pi\over3}=-60° \end{align}$$