Here's a link to Microsoft's Math program that you can download to your computer for no cost. It's basically a high-powered calculator that does the usual computation stuff, plus it graphs in 2-D or 3-D, solves equations with a Computer Algebra System (CAS), and even solves triangles.
Most of you will download and install the middle file (MSetup_x86.exe). That one is for a 32-bit system. The first file (MSetup_x64.exe) is for a 64-bit system. If you don't know what you have, ask your parents.