The breqn
package is a package that defines a set of new math environments, with the purpose of enabling automatic line breaking of displayed math. These new environments also let you have \left
and \right
on different lines, though it is not the main goal of the package.
Note that the package has several known problems and incompatibilities, so depending on your use case it might not be for you. I recommend a look at the manual.
The example below is one where you definitely shouldn't use \left
and \right
in the first place, but it serves to illustrate that it works. The dmath
environment is similar to equation
.

\documentclass{article}
\usepackage{geometry}
\geometry{a5paper, margin=5cm}
\usepackage{breqn}
\begin{document}
Automatic breaking:
\begin{dmath}
55 - \left(1+2+3+4+5+6+7+8+9+10\right) = 0
\end{dmath}
Manually breaking a line seems to work as well:
\begin{dmath}
55 - \left(1+2+3+4+\\5+6+7+8+9+10\right) = 0
\end{dmath}
\end{document}