Two plane mirrors make an angle of $30^{\circ}$ with each other. Locate graphically four images of a luminous point $A$ placed between the two mirrors. (See Fig. $36-6 .$ )
From A draw normals $A A^{\prime}$ and $A B^{\prime}$ to mirrors $O Y$ and $O X$, respectively, making $\overline{A^{\prime} N}=\overline{N A^{\prime \prime}}$ and $\overline{B^{\prime} P}=\overline{P B^{\prime \prime}}$.
Then $A^{\prime}$ and $B^{\prime}$ are images of $A$.
Next, from $A^{\prime}$ and $B^{\prime}$ draw normals to $O X$ and $O Y$, making $\overline{A^{\prime} N}=\overline{N A^{\prime \prime}}$ and $\overline{B^{\prime} P}=\overline{P B^{\prime \prime}} \therefore$ Then $A^{\prime \prime}$ is the image of $A^{\prime}$ in $O X$ and $B^{\prime \prime}$
is the image of $B^{\prime}$ in $O Y$.
The four images of $A$ are $A^{\prime}, B^{\prime}, A^{\prime \prime}, B^{\prime \prime}$. Additional images also exist, for example, images of $A^{\prime \prime}$ and $B^{\prime \prime}$.