Question 20
A ray of light originates from point $A$ and travels in a plane, being reflected $n$ times between lines $AD$ and $CD,$ before striking a point $B$ (which may be on $AD$ or $CD$) perpendicularly and retracing its path to $A.$ (At each point of reflection the light makes two equal angles as indicated in the adjoining figure. The figure shows the light path for $n=3.$) If $\angle CDA=8^\circ,$ what is the largest value $n$ can have?
