# MathJax: How to number and reference multiline equations?

I'd like to number multiline equations and reference them, à la MathJax's Align and Gather environments. Can this be accomplished? If so, how?

In the align environment, I use \tag to number. \label is also supported by MathJax. \ref can be used to reference a line using \label and \tag.

For example: $$\int_{-\infty}^\infty e^{-\pi x^2}\,\mathrm{d}x=1\label{a}\tag{1}$$ and reference it here: $\ref{a}$

• Thank you. Why is it that when I use \label in the align environment, the equations don't display but rather the underlying mathjax code? – Evan Aad Apr 8 '14 at 21:32
• @EvanAad: There seems to be a problem when editing. I find that when I save the edit and reload the page, things look okay. The same thing happened while I was editing my answer. – robjohn Apr 8 '14 at 21:33
• See this post for some details about why that is the case. Also, see the SOUP script for workarounds to this and many other small issues . – Davide Cervone Apr 8 '14 at 23:05
• But how was this done? I can't edit this answer, so I can't see the source code. – Daniel Martin Dec 2 '17 at 15:11
• @DanielMartin: I think that even if you can't edit an answer, you can right-click on a MathJax rendered formula and a pop-up will appear allowing you to choose "Show Math As > TeX Commands". – robjohn Dec 2 '17 at 15:27

In order to see the tags during edit, the following trick can be used.

\begin{aligned} a & = b & (1) \\ c & = d & (2) \end{aligned}

But now the equations cannot be hyperlinked to.