cross ratio

noun

, Geometry.

1. a ratio relating four points in the real or complex plane.

Other Words From

• cross-rati·o adjective

Word History and Origins

Origin of cross ratio¹

First recorded in 1880–85

Example Sentences

The identity of the locus of the A′s with the envelope of the a′s follows at once; moreover, a line meets the singular surface in four points having the same cross ratio as that of the four tangent planes drawn through the line to touch the surface.

From Project Gutenberg

It is generated by the lines which cut the faces of a tetrahedron in a constant cross ratio, and therefore by those subtending the same cross ratio at the four vertices.

From Project Gutenberg

The cross ratio of a range of four collinear points can now be defined as a number characteristic of that range.

From Project Gutenberg