## Projective Geometry## AbstractPerspectivity is the projection of objects from a point. A quantity that is preserved by this map, called the cross-ratio, naturally appears in many geometrical configurations. This map and its properties are very useful in a variety of geometry problems. We study the pole of a line, polar of a point, cross ratio, perspectivity, and we prove theorems of Desargue, Pappus, Pascal, Brianchon, and Brokard.
## Table of ContentsCross ratio. Harmonic conjugates. Perspectivity. ProjectivityDessargue\( \prime \)s theorem Theorems of Pappus and Pascal Pole. Polar. Theorems of Brianchon and Brokard Problems |

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