Thread: Non-Euclidian Geometry and Cross Ratios

I am taking a non-euclidian geometry class and it is killing me. I am trying to understand this stuff but it has been many years since I sat in a calculus or geometry class.

Here are my problems:

1. If (A,B;C,D) = r, show that (D,C;A,B) = 1/r

I am not familiar with cross ratios butcheck out wolfram's site on Cross Ratios

Please post if you get any further along.