cross ratio

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noun Geometry.

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

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Nearby words

cross one's mind, cross over, cross press, cross product, cross protection, cross ratio, cross reaction, cross reference, cross relation, cross river, cross river gorilla

Origin of cross ratio

First recorded in 1880–85

Also called anharmonic ratio.

Related forms

cross-ra·ti·o, adjective

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for cross ratio

If this cross-ratio equals −1 the four tangents are said to be four harmonic tangents.
Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6|Various
If we take the points in a different order, the value of the cross-ratio will change.
Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6|Various
The cross-ratio of any four points in one equals that of the corresponding points in the other.
Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6|Various
It is convenient to let the point at infinity occupy the last place in the symbolic expression for the cross-ratio.
Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6|Various

Before we draw conclusions from this result, we must investigate the meaning of a cross-ratio somewhat more fully.
Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6|Various