Question

in which mirror and in which lens focal length and radius of the curvature are postive and negative??​

Answer 1

Hence the radius of curvature and the focal length are positive for concave mirrors and negative for convex mirrors.

Answer 2

Hence the radius of curvature and the focal length are positive for concave mirrors and negative for convex mirrors.

By convention, distances are measured, along the central axis, as positive from the mirror in the direction of the object and negative away from the object. Hence the radius of curvature and the focal length are positive for concave mirrors and negative for convex mirrors.