GeometryDifficulty 6.0Prove itKöMaL problem A · Hungary · 2015
In the acute angled triangle ABC, the midpoints of the sides BC, CA and AB are D, E and F, respectively. The foot of the altitude of the triangle starting from C is T1. On some line, passing through point C but not containing T1, the feet of the perpendiculars starting from A and B are T2 and T3, respectively. Prove that the circle DEF passes through the center of the circle T1T2T3. Proposed by: Bálint Bíró, Eger (5 pont)
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