# align* but show one equation number at the end

I am using align*, but I still need an equation number. I know one solution is to use align and add \nonumber to all lines but the last. Is there a 'lazy' way to do it?

I searched a little and found similar ones suggesting use split: Show equation number only once in align environment

Unfortunately, due to the page break issue I have, I need to use align, because split won't auto page break, as described in Long equation does not page break.

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## 3 Answers

Use \tag:

\documentclass{article}
\usepackage{amsmath}
\newcommand\numberthis{\addtocounter{equation}{1}\tag{\theequation}}
\begin{document}
\begin{align*}
a &=b \\
&=c \numberthis \label{eqn}
\end{align*}
Equation \eqref{eqn} shows that $a=c$.
$$d = e$$
\end{document}


See page 3 of the amsmath package documentation for details.

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this \numberthis works beautifully. Thank you very much! –  cpp initiator Jan 29 '12 at 22:16
Why didn't you use \stepcounter or \refstepcounter instead of \addtocounter? –  Stiff Jokes Aug 31 at 6:14
@PSTikZ --- \refstepcounter isn't needed, as the \ref value is set correctly already. \stepcounter is probably the best choice, to take care of subsidiary counters. I don't think I gave much thought to this when I composed the answer. –  Ian Thompson Sep 2 at 8:25
OK. Thank you for responding! –  Stiff Jokes Sep 2 at 13:44
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Here are minimal working examples that I use. This is what I have as a header

\documentclass[12pt]{amsart}

\usepackage{amsmath,amsfonts,amssymb,epsfig}
\usepackage{graphicx}
\usepackage{hyperref}
%\usepackage{srcltx}
\hypersetup{colorlinks}
\usepackage{color}


Two equations each with separate equation numbers and separate reference labels

\begin{align}
\dot{a} &  =2\alpha(t)\eta\label{classicalmotion1}\\
\dot{\eta} &  =-2\gamma(t)a\label{classicalmotion2}%
\end{align}%


Two equations with single equation number and single reference label

\begin{aligned} \dot{A} & =2i\alpha(t)B\\ \dot{B} & =2i\gamma(t)A \end{aligned} \label{eqn2.qo}


I am guessing you know how to do the one without equation numbers.

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Just use the \nonumber option when using normal align before the end of every line but the last.

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If you read the OP's question carefully, he specifically mentions he is looking for a "lazy" way other than that. But welcome to TeX.SX! anyways! –  Xavier Jul 30 at 2:55
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