SG. 2 In $\triangle A B C, \angle B=\angle C=p^{\circ}$. If $q=\sin A$, find $q$.
$\begin{array}{l}\angle B=\angle C=75^{\circ}, \angle A=180^{\circ}-75^{\circ}-75^{\circ}=30^{\circ} \\ q=\sin 30^{\circ}=\frac{1}{2}\end{array}$