Mixing input formats - mathjax/MathJax-docs GitHub Wiki
All input formats can be mixed on the same page. You just have to watch out for delimiters -- for hopefully obvious reasons, you can't use the same delimiters for both TeX and asciimath...
The simplest way:
<script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-MML-AM_HTMLorMML"></script>
From https://groups.google.com/d/msg/mathjax-users/nDQ3PtJdaaM/yRsQUFHFGh0J, discussing LaTeX and asciimath input, sometimes it takes a long discussion