So the whole problem is:
If is the focal length of a convex lens and an object is placed at a distance from the lens, then its image will be at a distance from the lens, where and
are related by the lens equation
Suppose the focal length of a particular lens is 20cm. What is the rate of change of with respect to when ?
So to start out I plug in and into the equation above but then I can't figure what to do from here. I just having trouble comprehending the problem and figuring out how to start. Any help is greatly appreciated!