[Tex/LaTex] Subequations with main equation number

equationssubequations

I would like to have a set of equations, all under the same number, but with a "main" equation, and some other equations that follow being labelled with subnumbers, for example

1 = 1 (1)

1 < 2 (1a)

1 > 0 (1b)

How can I achieve this?

Best Answer

Use \tag for getting the main number:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{subequations}\label{first:main}
First some separate equations
\begin{equation}
1=1 \tag{\ref{first:main}}
\end{equation}
and another
\begin{equation}
1>0 \label{first:a}
\end{equation}
and another
\begin{equation}
1<2 \label{first:b}
\end{equation}
\end{subequations}

\begin{subequations}\label{second:main}
But it works also with \texttt{align} and the other alignment
environments
\begin{align}
1 &= 1 \tag{\ref{second:main}}\\
1 &> 0 \label{second:a}\\
1 &< 2 \label{second:b}
\end{align}
and you can reference all of them, as seen below.
\end{subequations}

Here are some references: \eqref{first:main}, \eqref{first:a}
and \eqref{second:b}.

\end{document}

enter image description here

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