Geometrical Optics

A ray of light travelling in the direction \({1 \over 2}\left( {\widehat i + \sqrt 3 \widehat j} \right)\) is incident on a plane mirror. After reflection, it travels along the direction \({1 \over 2}\left( {\widehat i - \sqrt 3 \widehat j} \right)\). The angle of incidence is