Frequently Asked Question List for TeX

# 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}
...

a=b
\label{eq1}

...
Remember that

a=b
\tag{\ref{eq1}}



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.

FAQ ID: Q-reuseq
Tags: math