3

I have an equation that looks like

y=4x \text{ for } x\in \{1,2\}

and would like to label it equation (1-2) so that the next equation in the paper is automatically labeled equation (3).

How can I do that?

1
  • Welcome to TeX.SE. I hope you'll be comfortable with us all.
    – Sebastiano
    Mar 29 '19 at 20:08
8

enter image description here

\documentclass{article}

\usepackage{amsmath}

\begin{document}

aaa \refstepcounter{equation}
\begin{equation}
  1=0 \tag{\theequation--\the\numexpr\value{equation}+1\relax}
\end{equation}

bbb\refstepcounter{equation}
\begin{equation}
  0 =1
\end{equation}
\end{document}
1

If you don't must to use sections, chapters, sub-sections, etc., a simple and fast solution it is uses a manual \tag for the first equation and automatic enumerate for other equations.

enter image description here

\documentclass[a4paper,12pt]{article}
\usepackage{mathtools}
\addtocounter{equation}{2}
\begin{document}
\begin{equation*}
x^2+y^2=1 \tag{1-2}
\end{equation*}
\begin{equation}
x^2+y^2=4
\end{equation}
\begin{equation}
\cos x +\sin x =1
\end{equation}
\end{document} 

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