# 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? Apr 8, 2014 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 Mod
Apr 8, 2014 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 . Apr 8, 2014 at 23:05
• But how was this done? I can't edit this answer, so I can't see the source code. Dec 2, 2017 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 Mod
Dec 2, 2017 at 15:27
• In the displayed equation you use \tag{1}. To refer to it you use \ref{a}. How does this work? I am not able to refer to \tagged equations. Am I missing the relevant part of MathJaX code? Oct 5, 2020 at 5:45
• @wdacda: The \label{a} is what is referenced by the \ref{a} which is displayed as $\ref{a}$.
– robjohn Mod
Oct 5, 2020 at 6:13
• @robjohn I get it now! With \tag{1} we control what will show as the "name" of the equation. We need the label to use it in \ref. Wonderful! I was quite slow. But better ever, then never. I prefer using \eqref, it is more like in math texts. Thank you! Oct 5, 2020 at 7:01

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.