Billiards, invisibility, and perfectly streamlining objects

In this paper we shall describe recent applications of billiards in aerodynamics
and optics. More precisely, we shall explain how to construct perfectly
streamlining bodies in the framework of Newtonian aerodynamics and invisible
objects in geometric optics. The methods we shall use are quite elementary
and accessible to students of the high school; they include focal properties of
curves of the second order and unfolding of a billiard trajectory.