render_math multiline equations

[wugh]

Hi, I want to use render_math to render multiline equation, because of my equation is too long.
But, I use follow code only generate online ugly equation.

$$\begin{align} f(x) & = (a+b)^2 \\ & = a^2+2ab+b^2 \\ \end{align}$$

[wugh]

just using \cr to break line, because of pelican markdown parser need to escape '', if we want to use '' to break line the we need \\\\