Problem

Source: 2020 Cono Sur Shortlist G4 https://artofproblemsolving.com/community/c1088686_cono_sur_shortlist__geometry

Tags: bisects segment, geometry, circumcircle



Let $ABC$ be a triangle with circumcircle $\omega$. The bisector of $\angle BAC$ intersects $\omega$ at point $A_1$. Let $A_2$ be a point on the segment $AA_1$, $CA_2$ cuts $AB$ and $\omega$ at points $C_1$ and $C_2$, respectively. Similarly, $BA_2$ cuts $AC$ and $\omega$ at points $B_1$ and $B_2$, respectively. Let $M$ be the intersection point of $B_1C_2$ and $B_2C_1$. Prove that $MA_2$ passes the midpoint of $BC$. proposed by Jhefferson Lopez, PerĂº