Problem

Source: Czech - Polish - Slovak Match 2013: P1

Tags: geometry, geometric transformation, homothety, LaTeX, cyclic quadrilateral, geometry unsolved



Suppose $ABCD$ is a cyclic quadrilateral with $BC = CD$. Let $\omega$ be the circle with center $C$ tangential to the side $BD$. Let $I$ be the centre of the incircle of triangle $ABD$. Prove that the straight line passing through $I$, which is parallel to $AB$, touches the circle $\omega$.