Question 200
Circles $k_{1}$ and $k_{2}$ intersect at points $A$ and $B$. Line $l$ is the common tangent to these circles and it touches $k_{1}$ at $C$ and $k_{2}$ at $D$ such that $B$ belongs to the interior of the triangle $ACD$. Prove that $\angle CAD + \angle CBD = 180^{\circ}$.