The Triangular Billiard Table Problem

Abstract

A ball is placed anywhere on a billiard table made in the form of an acuteangled triangle. It is required to find a point in a cushion such that if the ball is driven from its initial position to that point and then rebounds once each from the two other cushions it shall return to the point in which it hit the first cushion. It is understood that optical laws of reflection are obeyed and that the balls are points.