If perpendiculars AA', BB', and CC' are dropped to any line L from the vertices of a triangle ABC, then the perpendiculars A'A''. B'B'', and C'C'' to the opposite sides BC, AC, and AB, respectively, are concurrent at a point P called the orthopole of the line L and triangle ABC.
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Ten problems: 1411-1420
HTML5 and Dynamic Geometry
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