I found a way to display MathJax in an EverNote note -- but the trick
is to display it in WordPress. WordPress has plugins for both EverNote
(plugin is called EverPress) and MathJax. Set the EverPress plugin to
link to a shared notebook in your EverNote account (and whatever other
settings you want for displaying notes). When you want to include some
MathJax in a note, you need to double-escape the LaTeX commands -- so,
for example, instead of "\(\int e^x\, dx=e^x+C\)" in your note, write
it as "\\(\\int e^x\\, dx=e^x+C\\)". Then when the note displays in
WordPress (with the MathJax plugin), the LaTeX will be correctly
typeset in the WordPress page. Until someone finds a way to get the
EverNote site to actually use MathJax, this looks like the best option
available.
[ ref: discussion on EverNote User Forum
http://forum.evernote.com/phpbb/viewtopic.php?f=30&t=23658&start=25 ]
BTW -- I seem to be encountering this double-escaping hack a lot
lately, that is the same thing I had to do in order to get MathJax to
display correctly inside GWT widgets. It has to do with JavaScript
processing the strings before MathJax gets hold of them -- JavaScript
has its own set of escapes, for things like "\n" for newline
character, so to get "\" to show up at all in the next step (i.e. for
the MathJax). you have to use "\\".