In geometry, the orthopole of a system consisting of a triangle and a line in the same plane is a point determined as follows: Let , , be the feet of perpendiculars dropped on from , , respectively. Let , , be the feet of perpendiculars dropped from , , to the sides opposite , , (respectively) or to those sides' extensions. Then the three lines , , , are concurrent. The point at which they concur is the orthopole.
Due to their many properties, orthopoles have been the subject of a large literature. Some key topics are determination of the lines having a given orthopole and orthopolar circles.
Literature Orthopole=Ортополюс. In Russian
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