IMO Shortlist 1996 problem G1


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2. travnja 2012.
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Let ABC be a triangle, and H its orthocenter. Let P be a point on the circumcircle of triangle ABC (distinct from the vertices A, B, C), and let E be the foot of the altitude of triangle ABC from the vertex B. Let the parallel to the line BP through the point A meet the parallel to the line AP through the point B at a point Q. Let the parallel to the line CP through the point A meet the parallel to the line AP through the point C at a point R. The lines HR and AQ intersect at some point X. Prove that the lines EX and AP are parallel.
Izvor: Međunarodna matematička olimpijada, shortlist 1996