The formula to calculate the number of images formed by two plane mirrors when the angle between the two mirrors is given is:

$\text{Number of images}=\frac{360^{\circ }}{\text{angle between mirrors}}-1$

This formula assumes that the mirrors are set up in a way that they are facing each other and forming a closed reflective loop. The “-1” in the formula accounts for the original object itself.

For example, if the angle between the two mirrors is

$60^{\circ }$ $\text{Number of images}=\frac{360^{\circ }}{60^{\circ }}-1=5$

So, when two plane mirrors are set up at an angle of

$6{\mathrm{0\; degree }}^{}$

to each other, five images will be formed within the loop formed by the mirrors.