A triangle ABC with orthocenter H and altitudes AD, BF, and CE is inscribed in a circle O (see the figure below). DE cuts BF at G and the diameter BK cuts AC at M. Prove that HK and GM are parallel.
Geometry Problems Visual Index 1241-1250 Open Problems All Problems Triangles Circumcircle Altitude Orthocenter Circle Perpendicular lines Parallel lines View or Post a solution