You have learnt in the text how Huygens' principle leads to the laws of reflection and refraction. Use the same principle to deduce directly that a point object placed in front of a plane mirror produces a virtual image whose distance from the mirror is equal to the object distance from the mirror.

Explanation

From the object spherical wavefronts reach the reflector. Then reflected wavefronts are obtained from the mirror. One such wavefront that develops from the mirror in time t seconds is shown as reflected wavefront. If unreflected, in the absence of mirror, ADB is the position in the forward direction. Chord AB being thesame, the two arcs ADB and ACB should have their centres equidistant i.e., ON =NI i.e., the image is formed as far behind the mirror as the object is an front of it.