Using Huygen's principle, for a plane wavefront incident on a plane reflecting surface, draw the reflected wavefront. Hence prove laws of reflection.

$\displaystyle \Delta \mathrm{EAC}$ and $\displaystyle \Delta \mathrm{BAC}$ are congruent (RHS congruency ) $\displaystyle \therefore \angle \mathrm{i}=\angle \mathrm{r}$ The plane of mirror is ⟂ to plane of paper hence the incident ray, reflected ray and normal ray lie in same plane.