3 parallel lines + collinear related to intersections of circumcircles
Source: Sharygin 2011 Final 9.6
December 20, 2018
geometrycircumcirclealtitudecollinearcollinearityParallel Lines
Problem Statement
In triangle and are medians, and are altitudes. The circumcircles of triangles and meet again in point . Points are defined similarly. Prove that points are collinear and lines are parallel.