I need to identify and prove a theorem which can be proved in Euclidean geometry but not non-Euclidean. I need to have a diagram and explain why it works in Euclidean, but not in non-Euclidean.
I'm having trouble wrapping my head around this. It has been a long time since I've done this sort of thing! I know the difference between the two is the parallel postulate, the only Theorem that comes to mind is the Pythagorean Theorem, am I on the right track?
THank you for your help!
One result that comes immediately to mind is about the sum of all angles in a triangle adding up to a fixed number....