KaTeX is an alternative to MathJax. It's much, much faster than MathJax.

You can try it with the following demo. 45 ms vs 950 ms. KaTeX indubitably a winner.

To automatically render LaTeX equations you need to combine several document pages together (installation and auto-render plugin):

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.9.0-alpha1/katex.min.css" integrity="sha384-8QOKbPtTFvh/lMY0qPVbXj9hDh+v8US0pD//FcoYFst2lCIf0BmT58+Heqj0IGyx" crossorigin="anonymous">
<script src="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.9.0-alpha1/katex.min.js" integrity="sha384-GR8SEkOO1rBN/jnOcQDFcFmwXAevSLx7/Io9Ps1rkxWp983ZIuUGfxivlF/5f5eJ" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.9.0-alpha1/contrib/auto-render.min.js" integrity="sha384-cXpztMJlr2xFXyDSIfRWYSMVCXZ9HeGXvzyKTYrn03rsMAlOtIQVzjty5ULbaP8L" crossorigin="anonymous"></script>
<script>
  document.addEventListener("DOMContentLoaded", function() {
    renderMathInElement(document.body);
  });
</script>

And insert the following code into Blog Header section in Code injection admin page.

And two examples.

Mass-energy relation.

$$E=mc^2$$

And the Maxwell equations.

$$ \begin{aligned} \frac{\partial\mathcal{D}}{\partial t} \quad & = \quad \nabla\times\mathcal{H}, & \quad \text{(Loi de Faraday)} \\[5pt] \frac{\partial\mathcal{B}}{\partial t} \quad & = \quad -\nabla\times\mathcal{E}, & \quad \text{(Loi d'Ampère)} \\[5pt] \nabla\cdot\mathcal{B} \quad & = \quad 0, & \quad \text{(Loi de Gauss)} \\[5pt] \nabla\cdot\mathcal{D} \quad & = \quad 0. & \quad \text{(Loi de Colomb)} \end{aligned} $$

Looks awesome!