I just asked this question, but my inline math didn't work until I put a backslash before the dollar signs
Why is the backslash required? That isn't the case on other sites.
Sometimes, when MathJax is added to a site when it's mature and has a lot of posts already, Stack Exchange staff chooses to use
\$ delimiters instead of
$. This is to prevent things like
There are a few decent options in the $10-$20 range.
being displayed as
There are a few decent options in the \$10-\$20 range.
There are a handful of other sites in the network where this the case: for a complete list, see Which Stack Exchange sites use MathJax?.
Because when we added MathJax to the site, Stack Exchange staff decided to use
\$ as delimiters rather than
$ because many posts would be impacted otherwise. They cite an analysis by one of our citizens:
There are 349 posts that contain dollar signs, more than twice my estimate for posts that might benefit from MathJax (162). 137 of the 349 contain 2 dollar signs, if that matters.
— Miniman Nov 12 '15 at 0:37
(I know this doesn't really add much to Glorfindel's answer—really I just wanted to link both of those posts into this conversation, and my conscience wouldn't let me leave them in comments that really do answer the question.)