# cross ratio

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

## Origin of cross ratio^{}

First recorded in 1880–85

Also called anharmonic ratio.

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Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

## Examples from the Web for cross ratio

### Historical Examples

#### The cross-ratio of four points equals that of the four conjugate points.

#### Before we draw conclusions from this result, we must investigate the meaning of a cross-ratio somewhat more fully.

#### If we take the points in a different order, the value of the cross-ratio will change.

#### It is convenient to let the point at infinity occupy the last place in the symbolic expression for the cross-ratio.

#### The cross-ratio of any four points in one equals that of the corresponding points in the other.