## LaTeX forum ⇒ TeXworks ⇒ How to recall the equation (1)?

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yaozhao
Posts: 57
Joined: Sat Oct 27, 2018 10:38 pm

### How to recall the equation (1)?

$$MR=MC$$

Suppose this is the equation (2). In the article, I want to say, (2) can give us ......

How to recall (2)?

Maybe "recall" is not a good word here. Maybe retrieve?

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Stefan Kottwitz
Posts: 10164
Joined: Mon Mar 10, 2008 9:44 pm

### How to recall the equation (1)?

It's called referencing, and done by \label (to set a marker) and \ref or \eqref to reference that marker.
\documentclass{article}
\usepackage{amsmath}
\begin{document}
$$\label{anotherone} x = 2y$$
$$\label{myformula} MR=MC$$
\eqref{myformula} can give us...
\end{document}

Stefan

yaozhao
Posts: 57
Joined: Sat Oct 27, 2018 10:38 pm

### How to recall the equation (1)?

Hi Stefan,

I used your codes. But when I refer, LaTeX gives me (??).

\documentclass[a4paper, 12pt]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\DeclareUnicodeCharacter{202F}{\,}
In this way, we have the following equation in a perfectly competitive market:
$$\label{MR=P}MR=P$$

Remember, \eqref{MR=P} only holds in perfectly competitive market because price is only fixed in this type of market.\\

Stefan Kottwitz
Posts: 10164
Joined: Mon Mar 10, 2008 9:44 pm

### How to recall the equation (1)?

Run LaTeX two times. First time it reads all labels, the second time it inserts references.

Stefan