Answer
$-50^{\circ}$
Work Step by Step
First, ensure that your calculator is in radians.
On your graphing calculator, press the following sequence of buttons:
1. SIN$^{-1}$
2. (
3. -.766
4. )
5. ENTER
Therefore, $sin^{-1}(-.766)=-.873$ radians. Then, convert this number to degrees by multiplying by $\frac{180}{\pi}$.
$-.873radians=(-.873(\frac{180}{\pi}))^{\circ}=-50^{\circ}$.