When you open Calculator you'll only see the 4 basic functions and that's how it should be. By swiping left and right the panel changes and you're exposed to different branches of math. But if you don't need them it's as if they aren't there.

Calculator supports history graphing hex/bin conversion matrices and more. It won't solve equations for you but it gives you the tools to do so yourself as conveniently as it can.

This app is completely open source and comes bundles with some phones already.