The law of reflection is pretty simple, and not particularly enlightening. However, it will play a part in our discussion of mirrors, so we will include a brief description of it here.
Basically, the law of reflection says that a light ray and its reflection make equal angles with the normal to the reflecting surface:
Of course, the reflecting surface need not be flat; consider a circular reflector:
As the learned reader knows, rays along radii of a circle coincide with the normals to the circumference at those radii.