Online Geometry Problems

Online Geometry Problem 824: Desargues' Theorem, Triangles in Perspective, Concurrent Lines, Collinear Points, Center, Axis, Perspector, Perspectrix. Level: High School, SAT Prep, College, Mathematics Education


The figure shows the triangles ABC and A'B'C' so that AA', BB', CC' meet at a point O. AB and A'B' meet at D, AC and A'C' at E, BC and B'C' at F. Prove that D,E, and F are on a line (collinear points).
Note. The triangles ABC and A'B'C' are said to be in perspective, O is called the center of perspective or perspector. Line DEF is called the axis of perspective or perspectrix.


Geometry problem: Desargues theorem, perspective triangles


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