Question

why looking glasses are plane mirror?

Answer 1

the refletion that forms the image in plane mirror  is always erect lateraly inverted, but they are always virtual

Answer 2

hey.....
In contrast to plane mirrors, convex and concave mirrorscurve the rays of light that hit them. This results in the virtual images produced by their reflections coming out distorted, as the light rays move towards or away from the center of the mirror.
hope it help u...