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[ODC]=[HEA]=[GFB], find all values of C

Source: INMO 2013 P5

February 3, 2013
geometryrectanglegeometry proposed

Problem Statement

In an acute triangle ABC,ABC, let O,G,HO,G,H be its circumcentre, centroid and orthocenter. Let DBC,ECAD\in BC, E\in CA and ODBC,HECA.OD\perp BC, HE\perp CA. Let FF be the midpoint of AB.AB. If the triangles ODC,HEA,GFBODC, HEA, GFB have the same area, find all the possible values of C.\angle C.