You know from the law of reflection that when the line of sight reflects off the mirror, the angle of incidence equals the angle of reflection.

As it finally backs away through the glass, light doubling its loss through angles of reflection, your image doubles the distance between you—always twice as far from the source as you are ...

In this paper we develop a rigorous mathematical approach to overcome these difficulties involved and establish a global theory of existence and stability for shock reflection by large-angle wedges ...