Have you tried Wolfram Alpha? What are you waiting for?
If you get stuck doing homework problems often, have a hard time doing your classwork, or sometimes you just can't follow your lecture notes try going to Wolfram Alpha. Wolfram Alpha is a computational knowledge engine that is designed to handle mathematical problems and computation, and scientific problems. It has its limitations but it is a really awesome tool that gives a lot of detail when you need it. Try it out for yourself. http://www.wolframalpha.com