This site uses QuickLaTeX to produce LaTeX-syntax equations. To get equations inside a comment, just write [latexpage] (with the brackets) anywhere in your comment, and then include the usual LaTeX notation, i.e., $f_\alpha(x^2)$ becomes .
You can also use $$...$$, \[...\], \(...\), \equation, \align, \displaymath, \eqnarray, \multline, \flalign, \gather, and \alignat. In fact, if you really want, you write TikZ commands directly in the post using \begin{tikzpicture}...\end{tikzpicture}. QuickLaTeX will render them into images.
For more details, look here.
You can also use most of the simple HTML tags like the following:
- <b>bold</b> → bold
- <i>italics</i> → italics
- <a href="http://www.google.com">hyperlink</a> → hyperlink
A live preview of your comment will appear below the comment box, although LaTeX unfortunately may not render until you post. Luckily, comments can be edited after posting.