Question

f=r/2.is it applicable for both concave and convex mirror?

Answer 1

I think you’re confusing lenses and mirrors, and also upper and lower case. There’s no easy way to determine the focal length of a lens, and the relationship f = r/2 applies to mirrors.

So no, it doesn’t apply to any type of lens.

Answer 2

yes .

In both the spherical mirror,the focal length is half the radius of curvature .