I need some pure geometry :))
Source: IMO Shortlist 1996 problem G3
October 4, 2003
geometrycircumcirclesymmetrytrigonometryorthocenterIMO Shortlist
Problem Statement
Let be the circumcenter and the orthocenter of an acute-angled triangle such that . Let be the foot of the altitude of triangle . The perpendicular to the line at the point intersects the line at . Prove that .