### WT37: The cross ratio

The cross ratio is the most important invariant in projective geometry, and plays a key role in hyperbolic geometry. We introduce it here using vectors, that is in the framework of affine geometry. This video is part of the WildTrig series, which introduces Rational Trigonometry and applies it to many different aspects of geometry. This video is part of the WildTrig series, which introduces Rational Trigonometry and applies it to many different aspects of geometry.

Length:
10:11