# Reuse a previous equation with the original numbering [duplicate]

Here I am stuck again!

I have this equation 4.42 but I need to display this same equation, with this original number (4.42), in chapter 6. How can I do that?

The equation is:

\begin{equation} \label{Po}
\Pi=\pi-\frac{1}{3}c_s k_B T \phi \textbf{F}^2
\end{equation}


And below you can see the equation in chapter 4. How to put this equation in chapter 6, but enumerated 4.42?

• \begin{equation} \label{Po} \Pi=\pi-\frac{1}{3}c_s k_B T \phi \textbf{F}^2 \tag{\ref{<equation 4.42 label>}} \end{equation} ? in preamble should be loaded package amsmath . – Zarko Nov 27 '17 at 20:29

For example, \label and \ref can be used:

\documentclass{report}
\usepackage{amsmath}
\begin{document}
Chapter 4
\setcounter{chapter}{4}
\setcounter{equation}{41}

\begin{equation} \label{Po}
\Pi=\pi-\frac{1}{3}c_s k_B T \phi \textbf{F}^2
\end{equation}

Chapter 6
\setcounter{chapter}{6}

\begin{equation} \tag{\ref{Po}}
\Pi=\pi-\frac{1}{3}c_s k_B T \phi \textbf{F}^2
\end{equation}

\end{document} • Many thanks for helping me. That solved my problem. Have a nice week! – Ingrid Nov 27 '17 at 20:37
• And you beat me by 15 seconds -;). – AboAmmar Nov 27 '17 at 20:37

Add \tag{<ref. to original eq.>} to the equation in chapter 6 with reference to the original equation in chapter 4.

\documentclass[a4paper]{article}
\usepackage{amsmath}
\begin{document}

\begin{equation}\label{eq:one}
\begin{split}
A  = & \left( a + B + \right . \\
& \left.{} + c + d \right)
\end{split}
\end{equation}

\begin{equation} \label{repeated}\tag{\ref{eq:one}}
\Pi=\pi-\frac{1}{3}c_s k_B T \phi \textbf{F}^2
\end{equation}

\begin{equation} \label{Po}
\Pi=\pi-\frac{1}{3}c_s k_B T \phi \textbf{F}^2
\end{equation}

\end{document} • Thanks for your reply. I needed what Heiko Oberdiek did below. Have a nice week! – Ingrid Nov 27 '17 at 20:37
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