MathDB
BFG is a line

Source: Peru Cono Sur TST 2021 #3

August 27, 2022
geometrycircumcircle

Problem Statement

Let ABCABC be a triangle and DD is a point in BCBC. The line DADA cuts the circumcircle of ABCABC in the point EE. Let MM and NN be the midpoints of ABAB and CDCD, respectively. Let F=MNADF=MN\cap AD and GFG\neq F is the point of intersection of the circumcircles of DNF\triangle DNF and ECF\triangle ECF. Prove that B,FB,F and GG are collinears.