Let $ABC$ be an acute-angled, not equilateral triangle, where vertex $A$ lies on the perpendicular bisector of the segment $HO$, joining the orthocentre $H$ to the circumcentre $O$. Determine all possible values for the measure of angle $A$. (U.S.A. - 1989 IMO Shortlist)
Problem
Source: Stars of Mathematics 2011 - Juniors - Problem 2
Tags: geometry, perpendicular bisector, IMO Shortlist, geometry proposed
