> Personally, I wouldn't recommend Wolfram Alpha, or anything proprietary. If you have some programming knowledge (as OP is likely to), Sympy and Matplotlib are much more capable and controllable (and free!).

If one doesn't mind proprietary, though, and wants even more capable and controllable, Mathematica on a Raspberry Pi is pretty cool, and is free (beer) and is included in the default install of Raspbian.