# Using \left( & \right) around amsmath's align delimiter (“&”)

I want to align equations (using the align environment from the amsmath package) inside matching \left( and \right) commands. For example:

\documentclass[a4paper,12pt]{article}

\usepackage{amsmath}

\begin{document}

\begin{align}
a \left( b &= c \right)\\
d \left( e &= f \right)
\end{align}

\end{document}


But that code gives this error:

Extra }, or forgotten \right.

The error disappears when I remove the delimiters. Is there a workaround for this?

You cannot split \left...\right across alignment tabs. One solution is to use the \big-delimiters (which don't require pairwise usage):

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath

\begin{document}

\begin{align}
a \bigl( b &= c \biggr) \\
d \Bigl( e &= f \Biggr)
\end{align}

\end{document}


The above example is just to illustrate some delimiter sizes you can choose from. See section 4.14.1 Delimiter sizes of the amsmath user guide for more options:

Alternatively, one can adjust the alignment manually and avoid using & altogether. However, the above option is far easier to manage.

• This. Plus: never use \left and \right as long as you don't need to be bigger than Bigger – yo' Feb 14 '14 at 18:15

You can also accompany (i) \left( with \right. or (ii) \left. with \right). In other words,

\documentclass[a4paper,12pt]{article}

\usepackage{amsmath}

\begin{document}

\begin{align}
a \left( b \right. &=  \left. c \right)\\
d \left( e \right. &=  \left. f \right)
\end{align}

\end{document}


In that way, you will not obtain the error that you posted.

• Hi, welcome. The (potential) drawback of this is that it doesn't work well if b and c has different heights (try replacing c with \frac{a}{c}). You'll get different size parenthesis, unless you e.g. add a \vphantom{\frac{a}{c}} on the left side. – Torbjørn T. May 10 '17 at 18:34