Pages: Formula/Equation Editor

You can use Grapher.app (in /Applications/Utilities or via Spotlight), enter the formula there and then just copy&paste the formatted formula into Pages.

Pages does not have an equation editor by default. Apple does say, however, that if you have MathType 6 installed, you can use that from within Pages, and equations are then treated as graphics.

One option is to install a Latex distribution like MacTex and then use a small software called LatexIt.

It allows you to type equation with the full power of Latex without having to care about anything else of latex, you just type the equation and it generates a display of it that you can drag'n drop to your Page document, save in a standalone pdf or other format.