### Re-using an equation

To repeat an existing equation, one wants not only to have the same
mathematics in it, one also wants to re-use the original label it had.
The *amsmath* package comes to our help, here:

\usepackage{amsmath}
...
\begin{equation}
a=b
\label{eq1}
\end{equation}
...
Remember that
\begin{equation}
a=b
\tag{\ref{eq1}}
\end{equation}

Here, the second instance of a=b will be
typeset with a copy, made by the `\`

`tag`

command, of the label of the
first instance.

*amsmath.sty*- Distributed as part of AMSLaTeX
macros/latex/required/amslatex (or browse the directory); catalogue entry

This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=reuseq