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numbering few equations together

I am currently using an align environment to write a system of equations. The code has the form:

\begin{align*}\label{myEnv}
%equation 1 here
%equation 2 here
%equation 3 here
\end{align*}

I am wondering how I can number this environment using only a single number. Right now if I change align* back to align, I will get three different numbers for each line within the environment.

I know for a fact that \label{myEnv} returns the correct number, but I don't know how to display it within the actual LaTeX document.

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marked as duplicate by Peter Grill, Gonzalo Medina, Alan Munn, Thorsten, Joseph Wright Mar 29 '12 at 6:03

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1  
Perhaps try align with \nonumber for the lines you do not want to be numbered? –  André Mar 29 '12 at 1:12

2 Answers 2

This can be done with the split environment inside the align environment:

\documentclass{minimal}
\usepackage{amsmath}
\begin{document}
    \begin{align}\label{myEnv}
    \begin{split}
        equation 1 here \\
        equation 2 here \\
        equation 3 here 
    \end{split}
    \end{align}
\ref{myEnv} contains one number
\end{document}
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you can use:

\documentclass{minimal}
\usepackage{amsmath}
\begin{document}

For alignment use this:
        \begin{align}\label{myEnv}
        \begin{split}
            a &= b + c + d \\
            a &= b + c  \\
            av &= b + c
        \end{split}
        \end{align}
    \ref{myEnv} contains one number

For centered use this:
        \begin{align}\label{myEnv1}
        \begin{gathered}
            a = b + c + d \\
            a = b + c  \\
            av = b + c
        \end{gathered}
        \end{align}
    \ref{myEnv1} contains one number
    \end{document}
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