Problem

Source: 2022 IMOC G2 https://artofproblemsolving.com/community/c6h2918249p26069468

Tags: geometry, collinear, Concyclic



The incenter of triangle $ABC$ is $ I$. the circumcircle of $ABC$ is tangent to $BC$, $CA$, $AB$ at $T, E, F$. $R$ is a point on $BC$ . Let the $C$-excenter of $\vartriangle CER$ be $L$. Prove that points $L,T,F$ are collinear if and only if $B,E,A,R$ are concyclic. proposed by kyou46