Problem

Source: 2021 Saudi Arabia Training Lists p24 https://artofproblemsolving.com/community/c2758131_2021_saudi_arabia_training_tests

Tags: geometry, excenter



Let $ABC$ be triangle with $M$ is the midpoint of $BC$ and $X, Y$ are excenters with respect to angle $B,C$. Prove that $MX$, $MY$ intersect $AB$, $AC$ at four points that are vertices of circumscribed quadrilateral.