# label multiple lines of equations [duplicate]

Suppose I have the equations

\begin{align}
f(x) = x^2
g(x) = \exp( x )
\end{align}


I would like to use on single label for these lines, and ideally the equation number would be placed vertically between these two lines.

Although this question appears very basic, I have not found an explanation neither via search engines, nor on this website.

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## marked as duplicate by mafp, Stefan Kottwitz♦Mar 4 '13 at 14:58

Amsldoc is a good source for all equation-related things –  JLDiaz Mar 4 '13 at 13:47
there's an answer in this question: Show equation number only once in align environment –  barbara beeton Mar 4 '13 at 13:51

The very thing you want is the split environment, provided by the amsmath class.

Sample code.

\documentclass{article}
\usepackage[paperwidth=90mm]{geometry}% <-- better demonstrates the vertical alignment
\usepackage{amsmath}
\begin{document}

Eqn.~\eqref{eqn:eqlabel} has a single label split
across the two equations, as you can see here:
\begin{align}
\label{eqn:eqlabel}
\begin{split}
f(x) &= x^2 ,
\\
g(x) &= \exp( x ) .
\end{split}
\end{align}

\end{document}


Result.

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You can use an aligned or gathered environment inside an equation:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\label{eq:t} \begin{aligned} f(x) &= x^2\\ g(x) &= \exp( x ) \end{aligned}

$$\label{eq:u} \begin{gathered} f(x) = x^2\\ g(x) = \exp( x ) \end{gathered}$$

\end{document}

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