# How to put \dots in front equation numbers in amsmath

By default the style is

\renewcommand{\theequation}{\thechapter.\arabic{equation}}


for example

            x+y =4         (2.1)


How to put \dots in front equation numbering such as

            x+y =4      ...(2.1)


while in the text reference remain (2.1).

and how to make it for the array by using \begin{eqnarray} \end{eqnarray}

      x = y+ 4
-Z+ E
+ 4gh     ...(2.1)

• Welcome to TeX-SX! Have a look at our starter page for a quick intro if you wish to familiarize yourself with our format. – Claudio Fiandrino Jul 25 '13 at 6:26

The »mathtools« package provides the macros \newtagform and \usetagform which allow to do this quite comfortable.

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}

\usepackage{mathtools}  % loads »amsmath«
\newtagform{dots}{\ldots(}{)}

\begin{document}
$$(a+b)^2 = a^2+2ab+b^2 \label{eqn:binomi-one}$$
$$(a-b)^2 = a^2-2ab+b^2 \label{eqn:binomi-two}$$
$$\usetagform{dots} (a+b)(a-b) = a^2-b^2 \label{eqn:binomi-three}$$
%
The Binomi equations~\eqref{eqn:binomi-one},~\eqref{eqn:binomi-two} and~\eqref{eqn:binomi-three}.
\end{document}


Works of course also with the numbering scheme for equations in report and book.

• How about the \begin{eqnarray} \usetagform{dots} \end{eqnarray} , I try to use it but cant get it – YIT HOE NG Jul 25 '13 at 9:08
• @YIT HOE NG You shouldn't use eqnarray in your documents. You should use the environments provided by amsmath instead. – Gonzalo Medina Jul 25 '13 at 12:17
• @YITHOENG: Avoid eqnarray! I'm not aware of a solution that works inside the environments of »amsmath«. – Thorsten Donig Jul 25 '13 at 15:49

You can update the \maketag@@@ macro of amsmath to insert the \dots. Here's a convenience macro that you can add to your document preamble:

\makeatletter
\makeatother


It acts as a switch to enable "dotted equation numbering".

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\renewcommand{\theequation}{2.\arabic{equation}}% Just for this example
\makeatletter
$$f(x) = ax^2 + bx + c \label{eqn:one}$$
$$f(x) = ax^2 + bx + c \tag{xyz}\label{eqn:two}$$
$$\adddotsbeforeeqnnum f(x) = ax^2 + bx + c \label{eqn:three}$$