Answer
$\pi/5$
Work Step by Step
We know that the range of the inverse sine function is [-$\pi$/2, $\pi$/2], however, $11\pi/5$ is not in that range.
Subtracting $2\pi$ will give us the same angle, within the range of the inverse sine.
$11\pi/5 - 10\pi/5 = \pi/5$
and because $f^{-1}(f(x)) = x$, $\sin^{-1}(\sin(11\pi/5)) = \pi/5$.
