1. The problem statement, all variables and given/known data Hi everybody; a teacher of mine has given me a photo of two street lampd and their shadows; he has said to me that it's height is 3 metters, and the distance between the lamps is metters, and with that information I should be able to tell the lenght of the shadow. The image is taken from the top of a building, so I see the shadow making an angle with the lamp. 2. Relevant equations I have measured the distances of both, the shadow and the distance between lamps, which are 6.7 and 4.7 cm. 3. The attempt at a solution If I use a rule of three I can find the value of the lenght of the shadow, but the fact that the photo is taken from a certain height makes me uncomfortable, because I don't know if I am measuring the actual lenght or just a projection. Thanks for Reading.