This site uses QuickLaTeX to produce LaTeX-synatax 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