  An ancient optics problem of Ptolemy, studied later by Alhazen, is discussed.
This problem deals with reflection of light in spherical mirrors.
Mathematically this reduces to the solution of a quartic equation, which we
solve and analyze using a symbolic computation software. Similar problems have
been recently studied in connection with ray-tracing, catadioptric optics,
scattering of electromagnetic waves, and mathematical billiards, but we were
led to this problem in our study of the so-called triangular ratio metric.
