# How do you evaluate arcsin(sin((5pi)/3))?

$\arcsin$ and $\sin$ are inverses. Inverses, when applied on each other, cancel.
$x \cdot \frac{1}{x} = 1$, $\arcsin \left(\sin x\right) = x$, ${b}^{{\log}_{b} x} = x$, etc.
$\cancel{\arcsin} \left(\cancel{\sin} \left(\frac{5 \pi}{3}\right)\right) = \frac{5 \pi}{3}$