In Google Docs there is an equation editor that allows for users to insert math symbols into the document.  Unfortunately there is not an equation editor for Google Presentation.

A work around is Daum Equation Editor, a Chrome App that will launch in the Chrome web browser.

The Daum Equation editor works like most equation editors, a variety of templates for fractions, radicals, symbols and more.  After creating your equation, in the bottom right hand corner is an option to Save as Image.

On my Mac the Save as Image option does not add the .jpg file extension which is necessary to make the image file work.  Simply type .jpg at the end of the file name.

I save the image files onto my desktop so that I can drag the images directly from the desktop into the Google Presentation.

This is a relatively easy way to get math expressions into my Google Presentation.  The downside is that the expressions are images, thus not interactive.  If you need to make a change you will need to go back to the equation editor and create a new one.  But this is a relatively easy, and free, way for students to get math symbols in their Google Presentations.