1. The problem statement, all variables and given/known data An object is at a very large distance from a concave mirror of focal length 40cm. Find the distance from the image to the mirror. Is the image real or virtual? 2. Relevant equations 1/u + 1/v = 1/f 3. The attempt at a solution 1/u + 1/v = 1/40 The image has to be real because it must be outside the focus if it is very far from the mirror, right? It seems to me like I haven't got enough information to solve the problem. How would I go about doing it? The answer from the key is 40cm.