MathJax with AMS + Physics
AMS align (bundled by default):
$$ \begin{align} a^2 + b^2 &= c^2,\\ e^{i\pi} + 1 &= 0 \end{align} $$
Physics commands (require loader + packages config above):
$$ \dv{p}{t} = -\grad V(p) + F(t),\qquad \pdv{u}{x},\qquad \qty(\vb{E}\cdot\vb{B}) $$