Solve this:

​Q42. (i) A ray PQ of light is incident on the face AB of a glass prism ABC (as shown in the figure ) and emerges out of the face AC. Trace the path of the ray. Show that 
                    $\angle$i + ​$\angle$e = ​$\angle$A + ​$\angle$ $\delta$ 
        where, ​$\delta$ and e denote the angle of deviation and angle of emergence, respectively.
                   
      Plot a graph showing the variation of the angle of deviation as a function of angle of incidence. State the condition under which ​$\angle$ $\delta$ is minimum.