Wolfram
WolframAlpha.com is a website that allows you to input virtually any mathematical problem and it gives you a complete breakdown of solutions, graphs, alternate forms, and explanations. This should not take the place of learning and practicing the mathematics in your class. This will, however, give you a resource to deepen your understanding of these principles and offer a little aid if you get stuck. Please use this as a learning tool and not a crutch.
When typing in exponents use ^ for example x^2 is x to the second power.