How to get $\theta$ alone in $\sin2(\theta)$?

Question

$\sin2 \theta = (R \sin \phi)/2\cdot L$

I understand that the double angle formula brings $\sin2 \theta = 2\sin\theta \cos \theta$, however, I don't understand how to get $\theta$ alone on one side of the equation.

Answer 1

\begin{align} \sin(2\theta) & = (\cdots\cdots\cdots) \\[10pt] 2\theta & = \arcsin(\cdots\cdots\cdots) \\[10pt] \theta & = \frac 1 2 \arcsin(\cdots\cdots\cdots) \end{align}