MathDB
point moves along ray, line goes through fixed point

Source: Bulgaria 1988 P4

June 15, 2021
geometry

Problem Statement

Let A,B,CA,B,C be non-collinear points. For each point DD of the ray ACAC, we denote by EE and FF the points of tangency of the incircle of ABD\triangle ABD with ABAB and ADAD, respectively. Prove that, as point DD moves along the ray ACAC, the line EFEF passes through a fixed point.