1. Make a local copy of layouts/partials/header.html

This local copy will overwrite the copy in the theme when being built.

2. Insert the following code block at the top of the local copy of layouts/partials/header.html

<script type="text/x-mathjax-config">
    MathJax.Hub.Config({
        tex2jax: {
        inlineMath: [ ['$','$'], ["\\(","\\)"] ],
        processEscapes: true
        }
    });
</script>

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