Determine the focal length of a concave mirror if: (a) with the distance between an object and its image being equal to l = 15 cm, the transverse magnification β = – 2.0;
(b) In a certain position of the object the transverse magnification is β1 = – 0.50 and in another position displaced with respect to the former by a distance l = 5.0 cm the transverse magnification β = – 0.25.