If you have MathType 6.7d or later installed, you can use it to include mathematical expressions and equations in your spreadsheet.
Choose Insert > MathType Equation (from the Insert menu at the top of your screen).
Type or paste your equation in the field provided.
See MathType Help for instructions on using the MathType tools.
To save your equation, choose File > Close and Return to Numbers (from the MathType File menu at the top of your screen), then click Yes in the window that appears.
The equation appears in your spreadsheet. To edit the equation, double-click it to open MathType again.
You can change the look of the equation, move it, or delete it just as you can other images in your spreadsheet.