# How to label equation with particular format?

I have several equations, I want to label equation 1 and 2 to be (eqt1) and (eqt2), any other equations after it use normal equation number, say (1), (2), (3),... How to do it in latex?

E.g.

\begin{align}
1+1=2 (eqt1)
\end{align}

\begin{align}
2+3=5 (eqt2)
\end{align}

\begin{align}
3+3=6 (1)
\end{align}

\begin{align}
4+3=7 (2)
\end{align}

• That's the work for \tag{hello} – user156344 Jan 11 at 10:51
• please have a look at tex.stackexchange.com/questions/28894/modify-eqref-command – Yorgos Jan 11 at 10:53
• @Yorgos We can straightaway achieve it with \tag{...} (which is part of amsmath package) to customise the label of equations and then use the normal way of cross-referencing the equations with \eqref{...}. – Raaja Jan 11 at 10:54
• @Raaja oo nice... i didn't know this command, since i am using mathtools instead of amsmath – Yorgos Jan 11 at 10:57
• @Yorgos [Fun-fact] It is applicable for mathtools as well ;) – Raaja Jan 11 at 10:58

## 2 Answers

With amsmath package, you can achieve it with tag environment.

\documentclass[10pt,a4paper]{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
\label{e1}  1+1=2 \tag{eqt1}
\end{align}

\begin{align}
\label{e2}  2+3=5 \tag{eqt2}
\end{align}

\begin{align}
\label{e3}  3+3=6
\end{align}

\begin{align}
\label{e4}  4+3=7
\end{align}
I am referring \eqref{e1}, \eqref{e2}, \eqref{e3}, \eqref{e4}.
\end{document}


Which would give you

Another possibility, using the same equation counter as the default: mathtools has a \newtagform command, which can be used to customise the appearance of the equation number, and a \usetagform command which can be used within the document body:

\documentclass[10pt,a4paper]{article}
\usepackage{mathtools}
\newtagform{eqt}{(eqt\,}{)}

\begin{document}

\usetagform{eqt}
\begin{align}
\label{e1} 1+1=2
\end{align}

\begin{align}
\label{e2} 2+3=5
\end{align}

\usetagform{default}
\begin{align}
\label{e3} 3+3=6
\end{align}

\begin{align}
\label{e4} 4+3=7
\end{align}

\end{document}


• The OP asked for (eqt1), (eqt2), (1), (2). You have given them (eqt1), (eqt2), (3), (4). You would need to reset the counter after (eqt2) to give the behaviour asked for – lioness99a Jan 11 at 13:39
• This was not quite clear to me. I indeed mentioned that in what I propose, both types of equation share the same counter – only the formatting differs. – Bernard Jan 11 at 13:46
• They said they wanted to have (eqt1) and (eqt2) and then start counting from (1) again. Your answer continues counting after (eqt2) with (3) so you need to include \setcounter{equation}{0} at that point to get the behaviour the OP wanted – lioness99a Jan 11 at 14:02