How to Control Equation Numbering in LaTeX
LaTeX numbers equations automatically inside equation and align. Suppress a number with \nonumber (or \notag) before \\; force a custom label with \tag{...}; group lines as 1a, 1b with the subequations environment (amsmath). Reference an equation with \label and \eqref.
Example
\usepackage{amsmath}
\begin{align}
E &= mc^2 \label{eq:e} \\
F &= ma \notag
\end{align}
See \eqref{eq:e}.
\begin{subequations}
\begin{align}
a &= 1 \\
b &= 2
\end{align}
\end{subequations}Frequently asked questions
How do I remove the number from one equation?
Put \nonumber (or \notag) before the \\ on that line inside align, or use a starred environment (equation*, align*) to remove all numbers in the block.
How do I reference an equation?
Add \label{eq:key} on the line and cite it with \eqref{eq:key} (from amsmath), which prints the number in parentheses, e.g. (3).
How do I get sub-numbers like (1a) and (1b)?
Wrap the equations in the subequations environment from amsmath; each numbered inner line becomes 1a, 1b, and so on.
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