[Tex/LaTex] How to close \Big( with an invisible bracket

bracketsequations

When then opening and closing of a bracket are not on the same line, LaTeX demands 'invisible' brackets or it will get confused and not compile. Example:

\begin{equation}
\begin{aligned}
    A = 5 & \left(  a + b + c + ...  \right. \\  % The '\right.' is invisible but needed to close the 'left)
          & \left. d + e + f \right)         
\end{aligned}
\end{equation}

I noticed that this behaviour doesn't work when instead of using \left( you use \Big (or any similar bracket size expression). The following doesn't compile:

\begin{equation}
\begin{aligned}
    A = 5 & \Big(  a + b + c + ...  \right. 
          & \left. d + e + f \Big)       
\end{aligned}
\end{equation}

It gives the following error:

 ? Missing } inserted.
<inserted text> 
            }
l.20    A = 5 & \Big( a + b + c + ...  \right
                                            . \\
?

What does this mean and how can I solve it?

Best Answer

With \Big( (or better \Bigl( you do not need to close it: it is a self standing bracket.

\left \right are different in that they need to see the intervening expression as a single math list in order to determine the size to stretch, which is why they can not span different cells in an align.

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