The question is
"Prove that an interior point of a triangular pool table cannot be invisible."
pool table: a ray will bounce off a side such that angle of incidence = angle of reflection. If a ray hits a corner, the path ends there.
invisible: A point A in a polygon is called an invisible point if there is no pool shot from A coming back to A.
I'm thinking it is a proof by contradiction with some use of the Unfolding Principle. (Given a pool shot in some polygon P then we can unfold the pool shot to a straight line path by taking appropriate mirror images in the sides of P.
EDIT:// is it true that if a path doesn't include P, it would have to periodically not include P?
any sort of help will be appreciated. thank you in advance.