radius of curvature in case of plane mirror
Plane mirror Mathematically, a plane mirror can be considered to be the limit of either a concave or a convex spherical curved mirror as the radius, and therefore the focal length, becomes infinite.[4]
Rear-view mirror A rear-view mirror (or rearview mirror) is a mirror in automobiles and other vehicles, designed to allow the driver to see rearward through the vehicle's rear window (rear windshield).