I keep seeing people talk about mathjax on other posts by moderators etc. and it won't let me post/comment on there to ask what it is due to being new and not having enough reputation. So......what is mathjax?
It is a way to format mathematical things nicely. It is similar to $\LaTeX$ - I do not understand the differences. You enclose things in dollar signs and they look nice. For example if you want the stacked fraction 1/2 you write \frac 12 and put it in dollar signs to get $\frac 12$ You can right click on any MathJax on the site and select Show Math As -> TeX Commands to see how it was done. That is how I learned the basics. Web searching covered the finer points.
Mathjax is what we use on math.stackexchange.com to format mathematical formulas in a nice and easily-readable way. It is basically LaTeX syntax, with a few minor exceptions. For example, \$x\$ renders as $x$, \$f(x)>15x^2\$ as $f(x)>15x^2$.
You can find a tutorial here: MathJax basic tutorial and quick reference