Some telephoto cameras use a mirror rather than a lens. what radius of curvature mirror is needed to replace a 800 mm-focal length telephoto lens?

 R= 1.6 m

Explanation:

The radius of curvature of mirror and focal length is given by

                   R=2f

           where R is the radius of curvature

                      f is the focal length

As the telephoto camera uses mirror instead of lens , we can calculate the radius of curvature of mirror which has focal length of 0.8m which is same as that of lens.

          The radius of curvature of mirror is R =2*0.8

                         R= 1.6 m

a and b sometimes have a positive value

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.