Mathematically Speaking, Why do pool balss break at 90 Degree angles?

Question

I need to know why pool balls go off in two directions (creating a 90 degree angle) after making contact.

Answer 1

Website. The analysis is at the bottom of the page (scroll down).

Answer 2

In a break they go all over depending on how they are hit. When they hit the cushion they reflect back in the opposite direction at the same angle they go in at. When they hit each other it depends on the angle but momentum is transferred.