In any forum that discusses science, sooner or later it becomes necessary to include mathematical equations in your posts. Many forums (including the Peaceful Science forum for example, which uses the same Discourse software as here) offer LATEX support for this purpose. On such forums you can insert an equation by wrapping the LATEX markup in dollar signs, so for example:
Yeah, that’s what I came up with when I googled it, and I went to settings. There wasn’t anything about MathJax, just DiscourseMath, but I checked the four boxes available.
Or alternatively you can put it in a block (and split it up for clarity) using double dollar signs on their own lines:
$$
i \hbar \frac{d}{d t}\vert\Psi(t)\rangle
=
\hat H\vert\Psi(t)\rangle
$$
This will centre the equation like so:
i \hbar \frac{d}{d t}\vert\Psi(t)\rangle
=
\hat H\vert\Psi(t)\rangle
There are a whole lot of LATEX cheat sheets all over the web. This is one of the clearest that I found:
There’s also a Stack Exchange site for questions and answers about it:
Incidentally, Wikipedia also uses LATEX – if you want to cite a particularly common equation, you can always click “Edit” or “View source” on the Wiki page itself and copy and paste the markup from there.
LaTeX can build very complex math formulae. Unfortunately mathjax can’t quite do everything LaTeX math mode can do. BTW Don Knuth who developed TeX (the stuff under the hood for LaTeX) is a devout Lutheran.