### WT40: The fundamental theorem of projective geometry

The fundamental theorem of projective geometry states that any four planar non-collinear points (a quadrangle) can be sent to any quadrangle via a projectivity, that is a sequence of perspectivities. We prove this by first establishing the simpler one-dimensional case of three points on a projective line. This video is part of the WildTrig series, which introduces Rational Trigonometry and applies it to many different aspects of geometry.

Length:
09:17