Google Docs has an equation editor that has a fair number of options for symbols and functions available from the dropdown menu. All of these are also available through LaTeX macros that are conveniently listed† at Google Docs Support: Mathematical equations. However, this list is not complete. Some of the common amsmath functions that also work include:
Is there a list of all of the supported macros?
† Not at present, but Wayback Machine has a copy: https://web.archive.org/web/20160409034821/https://support.google.com/docs/answer/160749?hl=en