Answer
$ \frac{\pi}{9}$
Work Step by Step
$sin^{-1}[sin(-\frac{10\pi}{9})]=sin^{-1}[sin(2\pi-\frac{10\pi}{9})]=sin^{-1}[sin(\frac{8\pi}{9})]=sin^{-1}[sin(\frac{\pi}{9})]=\frac{\pi}{9}$
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