I have no idea how to use either of the Tex methods supported here.
How about putting a link to the instructions or a tutorial on both in the FAQ?
The advice from the question/answer in the proposed faq:
Q: How do I type math in my question/answer/comment?
A: For simple formulae, you can use
For more complicated formulae, you can use TeX markup.
To put the equation in its own line, surround with
AMS math environment is also supported, e.g.
Note that you need 4 backslashes for a new line. Many times you also need extra backslashes to avoid conflict with Markdown syntax, e.g.
If you are unfamiliar with TeX, you can find a question that uses the markup you'd like to use, then right click and select show source.
If you have detailed questions about TeX or LaTeX, this is not the appropriate place to ask them. Please use a dedicated TeX help site such as http://tex.stackexchange.com or http://www.latex-community.org/forum/
Feel free to edit or comment on the linked post if there is anything specific you'd like to see.
As for the official math.stackexchange faq, that can only be touched by a site admin, so it will take a while for the community proposed faq to propagate there.