Microsoft Math
Microsoft has had a good but generally unknown history of producing really quite remarkable Mathematics additions to its OS’s and Applications
Microsoft has just published a new version 4.0 get it here
Math contains
Graphing calculator
allows 2D and 3D colour graphing.
Formulas and Equations Library
more than 100 commonly used equations and formulae.
Triangle Solver
teaching tool for triangles and their parts.
Unit Conversion tool
convert units of measure, including length, area, volume, weight, temperature, pressure, energy, power, velocity, and time.
The Step-by-Step Equation Solver
helps learning on how to solve math problems.
The Main Site is here
Microsoft Mathematics Add-In for Word and OneNote get it here
I would definitely give it a spin
b.