1. The problem statement, all variables and given/known data A simple method for determining the focal length of a negative lens is shown below. Prove this is true. 2. Relevant equations 3. The attempt at a solution The linear magnification formula relates magnification, the distance from the lens to the image (i), the distance from the lens to the object (o) and the height of the two images (h'/h). The lens equation relates distance to the object and distance to the image and the focal length. I know I have to use these two equations but I have not been able to prove this is true. This is kind of frustating considering it's a simple problem, but can anyone point me in the right direction?