A short straight object of length L lies along the central axis of a spherical mirror, a

Question:

A short straight object of length L lies along the central axis of a spherical mirror, a distance p from the mirror.
(a) Show that its image in the mirror has a length L', where L' = L (f/p – f) 2.
(b) Show that the longitudinal magnification m' (= L'/L) is equal to m2, where m rs the lateral magnification.