Admin> Layout> Custom HTML in <head> section of every page:

<script type**=**"text/javascript"
src**=**"https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML">
</script>

<script type**=**"text/x-mathjax-config">
MathJax.Hub.Config({
extensions**:** ["tex2jax.js"],
jax**:** ["input/TeX", "output/HTML-CSS"],
tex2jax**:** {
inlineMath**:** [ ['$','$'], ["\\(","\\)"] ],
displayMath**:** [ ['$$','$$'], ["\\[","\\]"] ],
processEscapes**:** **true**
},
"HTML-CSS"**:** { availableFonts**:** ["TeX"] }
});
</script>