Cross-Ratio Four Points
The cross-ratio of four points in a line is equal to the cross-ratio of their projections on any other line which lies in the same plane with it.
Keywordsparallel lines, cross-ratio, cross-product, harmonic range, Chasles, anharmonic ratio, transversal
GalleriesGeometric Theorems and Proofs
Encyclopaedia Britannica (New York: The Encyclopaedia Britannica Company, 1910) 11:691