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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

Origin of cross ratio

First recorded in 1880–85

Also called anharmonic ratio.

Related formscross-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