MathNet 2017-part-06 — 176 problems (EN–VI) Question 15

Let $k$ be the circle circumscribed about $\triangle A B C$, and let $k_{a}$ be the excircle opposite vertex $A$. The two common tangents of the circles $k$ and $k_{a}$ intersect the line $B C$ at points $P$ and $Q$. Prove that $\varangle P A B=\varangle Q A C$.

(Dušan Đukić)