About: Orthologic triangles

In geometry, two triangles are said to be orthologic triangles if the perpendiculars from the vertices of one of them to the corresponding sides of the other are concurrent. This is a symmetric property, that is, if the perpendiculars from the vertices A, B, C of triangle ABC to the sides EF, FD, DE of triangle DEF are concurrent then the perpendiculars from the vertices D, E, F of triangle DEF to the sides BC, CA, AB of triangle ABC are also concurrent. The points of concurrence are known as the orthology centres of the two triangles.