Question

Prove that the cross ratio of four distinct points is never equal to one.​

Answer 1

In geometry, the cross-ratio, also called the double ratio and anharmonic ratio, is a number associated with a list of four collinear points, particularly points on a projective line. Given four points A, B, C and D on a line, their cross ratio is defined as

{\displaystyle (A,B;C,D)={\frac {AC\cdot BD}{BC\cdot AD}}} (A,B;C,D)={\frac {AC\cdot BD}{BC\cdot AD}}

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Answer 2

Answer:

Furthermore, let {Li | 1 ≤ i ≤ 4} be four distinct lines in the plane passing through the same point Q. Then any line L not passing through Q ...