Originally Posted by

**MacstersUndead** 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.

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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.