Light originates at a given point *P*(*a*,*b*), reflects off a mirror
at some point *R*, and reaches a given point *Q*(*c*,*d*).
It follows the path so that the
total distance traveled is minimum. Prove that the angle of incidence
equals the angle of reflection. Suggestion: Let be the
*x*-axis, and choose *P* and *Q* to lie above the *x*-axis.

Wed Apr 21 08:26:07 EDT 1999