If you are a student, then you must know the very powerful Equation function of Microsoft Word 2007. Extremely convenient for writing equations, the only thing it lacks is the ability to do the calculations…
Now with Microsoft Math Add-In for Word 2007, you can not only perform calculations but also have a Word equivalent of what the separate application Microsoft Math 2007 (bundled with Microsoft Student) offers.
The Microsoft Math Add-in for Microsoft Office Word 2007 makes it easy to create graphs, perform calculations, and solve for variables with equations created in Word.To use the add-in, open Word 2007, type Alt-= to create a RichEdit math object, type an equation or expression, and right-click on the equation to see options for solving and graphing within Word.
The Microsoft Math Add-in adds computational and graphing capabilities to the Equation Tools Ribbon of Word 2007.
With the Microsoft Math Add-in for Word 2007, you can:
- Plot a function, equation, or inequality in 2-D or 3-D- Solve an equation or inequality
- Calculate a numerical result
- Simplify an algebraic expression
Microsoft Math stuck?
No… it’s just that you need to specify whether the equation is in radians or degrees & whether you want complex or real numbers. 
Download here. (Validation & .Net Framework 2.0 required)
As a side-note, there’s also Equation Wizard that is quite good as Microsoft Math in solving equations…
Update:
Mathematics Add-In now available for Word 2010 & OneNote 2010. Download here.