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# Two plane mirrors are inclined to each other at some angle. A ray of light incident at $30^{\circ}$ on one mirror after reflection from the other mirror retracts its path. The angle between the mirror is :

$(a)\;30^{\circ} \\ (b)\;45^{\circ} \\ (c)\;90^{\circ} \\ (d)\;20^{\circ}$

Angle of incidence = angle of reflection $=30^{\circ}$
Since ray $ED$ returns its path it must fall normally
$\therefore \angle EDB= 90^{\circ}$
$\therefore \angle EOD= 90^{\circ}-60^{\circ}$
$\qquad= 30^{\circ}$
Hence a is the correct answer.