Carols 10cents is close, but you need to do the MathJax.Hub.Queue()
call in a callback from the jQuery load()
so that the typesetting isn't performed until after the file is loaded. (As it stands, it happens immediately after the file load is requested, even though the file may not be available yet). Something like
<script>
$(document).ready(function(){
$("#link").click(function(){
$("#myDiv").load("test.html", function () {
MathJax.Hub.Queue(["Typeset", MathJax.Hub, "myDiv"]);
});
});
});
</script>
See the examples from a talk I gave at the JMM in January 2013 for more details and the solution to other situations.