Answer
$\frac{\sqrt 3}{2}$
Work Step by Step
To find exact value of $\sin 120^{\circ}$, let's find its reference angle first. As $ 120^{\circ}$ terminates in quadrant II,
The reference angle = $ 180^{\circ} - 120^{\circ} $ = $60^{\circ}$
As $ 120^{\circ}$ terminates in quadrant II, its $\sin$ will be positive. Therefore by reference angle theorem-
$\sin 120^{\circ}$ = $\sin60^{\circ}$
= $\frac{\sqrt 3}{2}$
