The simplest way for everyone involved is probably using MathJax, if I’m not mistaken, this is also used on the Math StackExchange sites.
Searching the WordPress Plugin Repository I found MathJax-LaTeX and Simple Mathjax as well as other plugins.
Try those out, read the reviews, etc. and decide which to use on the site. The difference shouldn’t be too great. This will allow you to place code beautiful via
[latex]a^2 + b^2 = c^2[/latex]
$$ v = s \times a $$
$ 2 \times 3 = 9 $