The mirror box

Light rays bounce off mirrored walls of a square before reaching one of the other corners. What are the slopes of the light rays leaving A that land in one of the corners B or D after exactly k=5 reflections?

Scroll down for a solution to this problem.


The slope can be 1/6, 2/5, 3/4, 4/3, 5/2 and 6.

Solution by Stéphane Bernard.

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