This is a self-assigned question. Not homework. I may have the right answer, but would like some reviewing. It came to me while reading on a CS topic, this did not come from a math textbook, otherwise it would be slightly more in context. I did not use any formula (so 2 would be empty) and 1 and 3 are in a PDF here. 1. Is my work correct? 2. Is there an easier way to prove it? 3. What exactly is this? I called it an "'Arithmetic?' proof", but I don't think that this would be its name.