1. The problem statement, all variables and given/known data I'm currently in first year linear algebra... I'm doing quite well, there's just one area of trouble-- proofs. For example: Suppose u.v = u.w, does it follow that v = w? Prove your generalization. Prove that u is orthogonal to v - proju(v) for all vectors u and v in R^n where u != 0. Prove that (u + v) . (u - v) = ||u||^2 - ||v||^2 for all vectors u and v in R^n. There are about 20 questions in my current assignment in this format. I haven't been able to answer one of them to my satisfaction, whereas I currently have all non-proof questions correct. 2. Relevant equations This is the problem. It could be anything. I have hundreds of equations with these variables in them... But in a test situation, I couldn't possibly try all possible equations and see if they yield anything useful. 3. The attempt at a solution This is also a problem. I haven't the slightest clue where to start. If I had a beginning point, or a way to find a beginning point, I might actually be able to do these questions. :) Edit: perhaps there are some good websites that may have linear algebra proofs and other equations to practice with? There are so many sites out there, and the 20 or so I looked at today didn't have much material that I didn't already know... But there has got to be a good one somewhere.