Answer
$-\frac{\pi}{2}$
Work Step by Step
The angle between $-\frac{\pi}{2}$ and $\frac{\pi}{2}$ (including $-\frac{\pi}{2}$ and $\frac{\pi}{2}$) whose sine is -1 is $-\frac{\pi}{2}$.
$\arcsin (-1)=-\frac{\pi}{2}$
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