Orthopole
In geometry, the orthopole of a system consisting of a triangle ABC and a line ℓ in the same plane is a point determined as follows. Let be the feet of perpendiculars dropped on ℓ 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 References Points defined for a triangle