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.