Alight ray goes from a point a (in a medium of index n1) to a point b
(in a medium of index n2). the two media are separated by a dioptric plane surface.
the axis system is oxyz and the separation surface is the plane xoy, with a=(0,0,a)
and b=(d,0,-b).
by applying the fermat’s principle, find, in the xoy plane, the position of a point
m where the ray passes from medium (1) to medium (2). show that the 2 nd
descartes’ law is recovered.