# Equation numbering: how can I get (1.1), (2.1), (3.2) in the article class?

I know how to make them do 1, 2, 3....just need to know 1.1, 1.2, 3.2, 3.3 etc

\begin{align}

\end{align}


This will produce 1, 2, 3 etc, I know this but need the other.

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Use subequations. See (possible duplicates) How to reference equations using letters and numbers; How to number a set of equations separately from another set? – Werner Jan 19 '14 at 2:11
Welcome to TeX SE, your question could be made a little clearer. A minimal working example from \documentclass until \end{document} could enable more users to answer your question. – jens_bo Jan 19 '14 at 2:24
The title of you post is very bad. It is essentially useless for other users that may face a similar issue, when they search for existing questions/answers on this site. That would be nice if you could reformulate it in a more descriptive way, as, for instance: Equation numbering: how can I get (1.1), (2.1), (3.2) in the article class? – pluton Jan 19 '14 at 5:26

The amsmath package offers you the subequations environment; to get the desired formatting, you can redefine \theequation:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{subequations}
\begin{align}
y & = d \\
y & = cx+d \\
y & = bx^{2}+cx+d \\
y & = ax^{3}+bx^{2}+cx+d
\end{align}
\end{subequations}

\begin{subequations}
\renewcommand{\theequation}{\theparentequation.\arabic{equation}}
\begin{align}
y & = d \\
y & = cx+d \\
y & = bx^{2}+cx+d \\
y & = ax^{3}+bx^{2}+cx+d
\end{align}
\end{subequations}

\end{document}


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The question can also be interpreted that the first number of the composite equation number should be the section number. The other two classes report and book are using composite equation numbers, whose first part is the chapter number. The article class does not have chapters and uses plain equation numbers.

Package amsmath (this is used because of align) provides an easy way to add the section number:

\numberwithin{equation}{section}


Complete example:

\documentclass{article}
\usepackage{amsmath}

\numberwithin{equation}{section}

\begin{document}
\section{Equation numbering}
\begin{align}
a = a\\
b = b\\
c = c
\end{align}

\section{Second section}
\begin{gather}
d = d
\end{gather}
\end{document}


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