Add math: true
to the page markdown header followed by embedding this javascript:
<script type="text/javascript"
src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?config=TeX-AMS_CHTML">
</script>
Inline math:
$ \varphi = \dfrac{1+\sqrt5}{2}= 1.618033988 $
Block math:
$$
\tag{1.1}
\sigma(t) = \cfrac{1}{1 + e^{-t}}
$$