In Windows 7, Microsoft Word 2007 and 2010 offer builtin equation tools, which help you build complex mathematical formulas that include abnormal characters such as exponents, radicals, fractions, integrals, matrices and other advanced arithmetic operators, functions and characters. Previous versions of Word offered only an addin equations editor, Microsoft Equation 3.0, and any documents saved in .doc format must use this equation editor. Word 2007 and 2010 contain both the builtin equation tools and the older equation editor.
Create New Equation

Click, in the text of the document, where you want to place the equation.

Click the "Insert" tab on the Ribbon.

Click the "Equation" button on the Ribbon  its icon is a "Pi" symbol. When you click it, Word automatically inserts a new equation and opens the equations editor.

Create your equation. To add numbers, type them on your keyboard. To add a special symbol or character, scroll through the Symbols menu on the Ribbon and click the one you want to add. To create special formulas such as fractions, radicals or operators, use the buttons on the right section of the Ribbon; these buttons offer dropdown menus, from which you can choose the specific structures you want.

Click on the page outside the equation when you want to close the equation tools. The equations editor on the Ribbon will close and the "Design" tab will disappear, but don't worry; the Ribbon will display this tab again any time you click on the equation.
Edit Equation in .Docx

Click on the equation. The "Design" tab will appear on the Ribbon, either open or simply available.

Click the "Design" tab on the Ribbon, if it did not open automatically.

Use the tools, symbols and structures provided on the Ribbon to edit the equation.

Click on the page outside the equation when you want to close the equation tools.
Edit Equation in .Doc

Doubleclick on the equation, which opens the equation editor.

Edit the equation using the tools provided in the equation editor toolbar.

Click on the page outside the equation when you want to close the Equation Editor.
Tips & Warnings
 If you want to use the builtin equations tools, but you can't use them for your document (the "Equation" button will appear gray and unclickable), then convert the document to .docx.
References
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