# 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:

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


And below you can see the equation in chapter 4.

How to put this equation in chapter 6, but enumerated 4.42?

• $$\label{Po} \Pi=\pi-\frac{1}{3}c_s k_B T \phi \textbf{F}^2 \tag{\ref{<equation 4.42 label>}}$$ ? 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}

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

Chapter 6
\setcounter{chapter}{6}

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

\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}

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

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

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

\end{document}


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