I'm planning a couple of posts that will require writing equations. As the title suggests I'm using MathJax to render equations into HTML.

Final code injection in Ghost > Code Injection > Head
<script type="text/javascript" async src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.3/MathJax.js?config=TeX-MML-AM_CHTML">
MathJax.Hub.Config({
    tex2jax: {
        inlineMath: [["$", "$"], ["\\(", "\\)"]],
        processEscapes: true
    }
});
</script>

Helpful Posts:

Examples with Markdown and rendering

$$\sum_{i=0}^n i^2 = \frac{(n^2+n)(2n+1)}{6}$$

$$\sum_{i=0}^n i^2 = \frac{(n^2+n)(2n+1)}{6}$$
Inline Equation: $\sum_{i=0}^n i^2 = \frac{(n^2+n)(2n+1)}{6}$
Inline Equation: $\sum_{i=0}^n i^2 = \frac{(n^2+n)(2n+1)}{6}$
Matrices
$$ A=\begin{bmatrix} a & b\\ c & d\\ e & f \end{bmatrix} $$
<div> 
    $$
    A=\begin{bmatrix}
    a & b\\
    c & d\\
    e & f
    \end{bmatrix}
    $$
</div>
Bayes Theorem
\begin{equation} \label{eq:bayes} P(\theta|\textbf{D}) = P(\theta ) \frac{P(\textbf{D} |\theta)}{P(\textbf{D})} \end{equation}
<div>
    \begin{equation}
    \label{eq:bayes}
    P(\theta|\textbf{D}) = P(\theta ) \frac{P(\textbf{D} |\theta)}{P(\textbf{D})}
    \end{equation}
</div>