cross ratio

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

QUIZZES

Have the Words of the Day from October 19–25, 2020, made an indelible mark on your memory? Take the quiz to find out!

Question 1 of 7

What does “clement” mean?

Also called anharmonic ratio .

First recorded in 1880–85

cross-ra·ti·o, adjective

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