How to put equation number only at the last step of a multi-line calculation?

I have to write a calculation that takes two lines. I need to put number only at the last step. How do I do that? I used \nonumber at the end of the first line where I don't want to put equation number. But the number is being shown on the first line and not on the last line.

for example:

\begin{eqnarray}
\dot{\epsilon}&=& u_\mu u_\nu\Bigl(\dot{I}^{\mu\nu}_{(0)+}+\dot{I}^{\mu\nu}_{(0)-}\Bigr)\\
&=& u_\mu u_\nu\int\mathrm{dp}~p^\mu p^\nu\bigl(\dot{f}_{(0)}+\dot{\bar{f}}_{(0)})
\label{eq:1}
\end{eqnarray}

• Can you please show an example of code? – egreg Apr 18 '18 at 9:04
• i have added the code but, I don't know how to write like LaTex in here. So, I just copy pasted it. – Samapan Bhadury Apr 18 '18 at 9:08
• That's the correct way; we don't use MathJax here because we're interested in TeX/LaTeX code. You paste the code, select it and click on the {} small icon on the top of the editing box. – egreg Apr 18 '18 at 9:12
• for future purpose can tell me how did you do it? – Samapan Bhadury Apr 18 '18 at 9:13
• Adding four spaces in front of each row activates the syntax highlighting. There is also a button in the toolbar that helps you adding these four spaces for a larger amount of selected lines. – Tiuri Apr 18 '18 at 9:16

Don't use eqnarray ! It yields bad spacing. Replace it with one of the amsmath environments. Here you can use an aligned environment, with option [b], nested in equation:

\documentclass[11pt]{article}

\usepackage{amsmath}

\begin{document}

\begin{aligned}[b] \dot{\epsilon}&= u_\mu u_\nu\Bigl(\dot{I}^{\mu\nu}_{(0)+}+\dot{I}^{\mu\nu}_{(0)-}\Bigr)\\ &= u_\mu u_\nu\int\mathrm{dp}~p^\mu p^\nu\bigl(\dot{f}_{(0)}+\dot{\bar{f}}_{(0)}) \end{aligned} \label{eq:1}

\end{document}


\nonumber at the end of the first line works. But be careful: At the end of the first line means before the line-breaking \\ that ends the first line.

MWE:

\documentclass{article}
\begin{document}
\begin{eqnarray}
\dot{\epsilon}&=& u_\mu u_\nu\Bigl(\dot{I}^{\mu\nu}_{(0)+}+\dot{I}^{\mu\nu}_{(0)-}\Bigr) \nonumber\\
&=& u_\mu u_\nu\int\mathrm{dp}~p^\mu p^\nu\bigl(\dot{f}_{(0)}+\dot{\bar{f}}_{(0)})
\label{eq:1}
\end{eqnarray}
\end{document}


• Okay thanks. I was using it wrong. I was putting the \nonumber after the '\\'. that is why it was not waotking. – Samapan Bhadury Apr 18 '18 at 9:15

You should never use eqnarray, the reasons are explained at eqnarray vs align and they should also be clear from a visual comparison. I also made some small changes, notably to the dimension of the parentheses and to the treatment of differentials.

\documentclass{article}
\usepackage[tbtags]{amsmath}

\newcommand\prediff[1]{\mathrm{d}#1\,}
\newcommand{\diff}{\mathop{}\!\mathrm{d}}

\begin{document}

This is not the best way to cope with the problem:
\begin{eqnarray}
\dot{\epsilon}&=& u_\mu u_\nu\Bigl(\dot{I}^{\mu\nu}_{(0)+}+\dot{I}^{\mu\nu}_{(0)-}\Bigr)\nonumber\\
&=& u_\mu u_\nu\int\mathrm{dp}~p^\mu p^\nu\bigl(\dot{f}_{(0)}+\dot{\bar{f}}_{(0)})
\label{not-the-best}
\end{eqnarray}
Perhaps you are better served with \texttt{split} (note
the option \texttt{tbtags}):
$$\label{better} \begin{split} \dot{\epsilon} &= u_\mu u_\nu\bigl(\dot{I}^{\mu\nu}_{(0)+}+\dot{I}^{\mu\nu}_{(0)-}\bigr)\\ &= u_\mu u_\nu\int\prediff p p^\mu p^\nu\bigl(\dot{f}_{(0)}+\dot{\bar{f}}_{(0)}) \end{split}$$
With the differential at the end it would be
$$\label{better-post} \begin{split} \dot{\epsilon} &= u_\mu u_\nu\bigl(\dot{I}^{\mu\nu}_{(0)+}+\dot{I}^{\mu\nu}_{(0)-}\bigr)\\ &= u_\mu u_\nu\int p^\mu p^\nu\bigl(\dot{f}_{(0)}+\dot{\bar{f}}_{(0)})\diff p \end{split}$$

\end{document}