You've enabled the plugin!?
katex plugin problem

Why I am not able to render matrix through plugin when I am writing my latex inside //(//).
Latex code I am writing is :
\begin{bmatrix}a & b \c & d \end{bmatrix} 
Another way is to put the following into your custom header:
<script type="text/xmathjaxconfig"> MathJax.Hub.Config ({tex2jax: {inlineMath: [['$','$'], ['\\(','\\)']], skipTags: ["<pre>","<span>"] }, TeX: {equationNumbers: {autoNumber: "AMS"}, extensions: ["color.js"], Macros: {ra: "{\\rm a}", rb: "{\\rm b}", rgh: "{\\rm rgh}", rD: "{\\rm D}", cell: "{\\rm cell}", drag: "{\\rm drag}", lift: "{\\rm lift}", rd: "{\\rm d}", Kd: "{\\rm Kd}", rc: "{\\rm c}",rN: "{\\rm N}",tr: "{\\rm tr}",dev: "{\\rm dev}",mag: "{\\rm mag}",max: "{\\rm max}",min: "{\\rm min}",exp: "{\\rm exp}", rq: "{\\rm q}", rE: "{\\rm E}", dpm: "{\\rm dpm}", rT: "{\\rm T}",rP: "{\\rm P}", rW: "{\\rm W}", bfU: "{\\bf U}", bfHbyA: "{\\bf HbyA}", bfS: "{\\bf S}", bfg: "{\\bf g}", bfh: "{\\bf h}", bfT: "{\\bf T}", bfV: "{\\bf V}", bfd: "{\\bf d}", bfI: "{\\bf I}", bfK: "{\\bf K}", bfA: "{\\bf A}", bfn: "{\\bf n}", bfR: "{\\bf R}", bfM: "{\\bf M}", bfx: "{\\bf x}",bfF: "{\\bf F}", p: "{\\partial}" } } } ); </script> <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeXAMSMML_HTMLorMML"> </script> <script> $(window).on('action:posts.loaded action:ajaxify.end', function () { MathJax.Hub.Queue(["Typeset", MathJax.Hub, "content"]); }); </script>
then you can use MathJax.