Eric Danneels and Nikolaos Dergiades, A Theorem on Orthology Centers,
Forum Geometricorum, 4 (2004) 135--141.

Abstract:  We prove that if two triangles are orthologic, their orthology centers have the same barycentric coordinates with respect to the two triangles. For a point P with cevian triangle A'B'C', we also study the orthology centers of the triangle of circumcenters of PB'C', PC'A', and PA'B'.

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