This is an old post, go to https://www.texthelp.com/en-us/products/equatio/ to find about the replacement for gMath.
Something that some people did not like about Google Docs was the lack of an in-depth math equation editor as they were accustomed to in Word. Through the use of a new Add-on, you can get a lot of the same functionality to combine with the collaborative aspect of Google Docs. You can even use this Add-on in a spreadsheet to create a Google Form for some formative assessment with students. The best part is that students can use this too on their devices for them to create and share.
There is a separate Add-on for both Google Docs and Google Sheets, each having very similar abilities but with some different features based on whether it is a Doc or Sheet. Install the Add-on by going to the Add-ons tab and select “Get Add-ons” to find it in the Add-on store. Once installed on one document, it is available on all of your docs. You do need to install it separately on a Sheet but once it is installed on a Sheet, it is available on all Sheets.
To use the gMath Add-on in a Google Doc you just have to go to Add-ons and select it from the list. Right now, since gMath is constantly getting new features and is being updated based on needs from the users, you have 3 options; create math expressions, create a graph, or create a statistical display.

Each gives you different options on what you insert into the Doc. With the math expressions you can easily insert an equation or edit a previously used equation by using the formats given to you or you can even use any LaTeX code for creating the math equation. There are a lot of pre-made formats available to make it easier to insert and the addition of the ability to edit previous equations make it nice to come back to it later.
To go from inserting an expression to inserting a graph you do need to go back to the gMath option under Add-on and select the new format. Now you will be able to graph equations or insert a graph of data points into the doc.
The biggest addition to what you can do differently in a Google Sheet is the ability to create a Google Form with math expressions or graphs as part of the question. This can be used to easily create formative assessments to use with students.
You can find a lot of information about the gMath Add-on from the site of the creator of the Add-on (http://mathtechtips.blogspot.com/) and you can see how to get started by watching the video below.
google sucks they don’t have it anymore
Actually, it has been updated and is called Equatio and you can find more about it at https://www.texthelp.com/en-us/products/equatio/