Often I have a chain of equations but later on I only want to refer that the first statement is equal to the last one. There are some options to do that:

```
\begin{align}
\label{equation}
a
&= b \\
&= c \\
&= d \\
&= e \\
&= f
\end{align}
Equation~\eqref{equation} gives $a=f$.
\begin{align}
a \label{equation_first}
&= b \\
&= c \\
&= d \\
&= e \\
&= f \label{equation_last}
\end{align}
Equation~\eqref{equation_first}--\eqref{equation_last} gives $a=f$.
\newcommand\numberthis{\addtocounter{equation}{1}\tag{\theequation}}
\begin{align*}
a
&= b \\
&= c \\
&= d \\
&= e \\
&= f \numberthis \label{equation2}
\end{align*}
Equation~\eqref{equation2} gives $a=f$.
\begin{equation}
\label{equation_split}
\begin{split}
a
&= b \\
&= c \\
&= d \\
&= e \\
&= f
\end{split}
\end{equation}
Equation~\eqref{equation_split} gives $a=f$.
```

- The first one is just bad, as (2)–(5) are displayed, but not included in the reference.
- The second one is more or less okay, but after all it is
*one*equation while it looks like I need six equations. - The third one is a hack I found here (alternativly I could have used
`align*`

and lots of`nonumber`

s). This version is okay, but does not look that good. Sure, I could put the tag on the center line, but thatâ€˜s manual work (I have to (not forget to) redo that stuff after adding some lines) and there is not always a center line. - The fourth option looks quite good. However, I pretty much always used
`align[*]`

up to now. Are there any problems with`equation+split`

?

How do you tag multi line equations? Why?

## Best Answer

You could use the

`aligned`

environment:It centers the number vertically even if the number of equations is even, and the reference works fine.