Question 5
In plane, let be given two circles intersecting at $A$ and $B$ and let $PQ$ be a common tangent ($P$ and $Q$ are touching points). Let $S$ be the point of intersection of the tangents at $P$ and at $Q$ of the circumcircle of triangle $APQ$ and let $H$ be the reflection of $B$ in the line $PQ$. Prove that the points $A$, $S$, $H$ are collinear.