compute the cross ratio (or anharmonic ratio, or double ratio) of four points
CrossRatio(A, B, C, F)
A, B, C, F
Given four points A, B, C, F, the routine CrossRatio(A, B, C, F) computes the cross ratio of A, B, C, F taken in this order.
If A, B, C, F are four distinct points on an ordinary line, the cross ratio of A, B, C, F taken in this order is defined as:
The command with(geometry,CrossRatio) allows the use of the abbreviated form of this command.
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