Problem

Source: Indonesia INAMO Shortlist 2017 G9 https://artofproblemsolving.com/community/c1101409_indonesia_shortlist__geometry

Tags: geometry, angle bisector, cyclic quadrilateral, parallelogram, equal segments



It is known that $ABCD$ is a parallelogram. The point $E$ is taken so that $BCED$ is a cyclic quadrilateral. Let $\ell$ be a line that passes through $A$, intersects the segment $DC$ at point $F$ and intersects the extension of the line $BC$ at $G$. Given $EF = EG = EC$. Prove that $\ell$ is the bisector of the angle $\angle BAD$.