Error: Extra }, or forgotten \right while keeping the correct hight of brackets

Question

The following works fine,

\begin{equation*}
    \begin{aligned}
        \begin{split}
            \left\| \left(a - c\right) - \frac{|b|^2\cdot |d|^2}{|b \times d|^2} \left[
                                     \left(\left(a - c\right)\cdot \left(\frac{b}{|b|} - \frac{b \cdot d}{|b|\cdot|d|} \cdot \frac{d}{|d|}\right)\right) \cdot \frac{b}{b} \right.\right. + \\
            \left.\left. \left(\left(a - c\right)\cdot \left(\frac{d}{|d|} - \frac{b \cdot d}{|b|\cdot|d|} \cdot \frac{b}{|b|}\right)\right) \cdot \frac{d}{d} 
            \right] \right\| = \frac{|(a - c) \cdot b \times d|}{|b \times d|}  
        \end{split}
    \end{aligned}
\end{equation*}

but if I add &, it throws an error

\begin{equation*}
    \begin{aligned}
        \begin{split}
            \left\| \left(a - c\right) - \frac{|b|^2\cdot |d|^2}{|b \times d|^2} \left[
                                     & \left(\left(a - c\right)\cdot \left(\frac{b}{|b|} - \frac{b \cdot d}{|b|\cdot|d|} \cdot \frac{d}{|d|}\right)\right) \cdot \frac{b}{b} \right.\right. + \\
            & \left.\left. \left(\left(a - c\right)\cdot \left(\frac{d}{|d|} - \frac{b \cdot d}{|b|\cdot|d|} \cdot \frac{b}{|b|}\right)\right) \cdot \frac{d}{d} 
            \right] \right\| = \frac{|(a - c) \cdot b \times d|}{|b \times d|}
        \end{split}
    \end{aligned}
\end{equation*}

According to many posts, I tried several combinations of \begin{equation*}, \begin{aligned}, \begin{split} and \begin{multline*} but without success. What do I miss?

Expected result

(Without & the first square bracket is also ok, but the alignment is destroyed)

Comment, why this is not a duplicate of other questions: To me, the crucial point of the answer is, that you need an extra \vphantom{\frac{b}{b}}\right.\right. and you have to add another & \left.\left. line.

You can't put an alignment symbol & between \left and \right. — campa, Apr 26 '19 at 12:26
@campa, no, see my edit. I tried and the solution there does not work. I think, there is no way around the trick suggested in the solution below. — Christoph, Apr 26 '19 at 12:45
@AndrewSwann: OK, if you understand the problem, you know, the comment at the bottom of the page is crucial ;-) Perhaps it would be good to add that point to the answer below? — Christoph, Apr 26 '19 at 14:24

score 2 · Answer 1 · answered Apr 26 '19 at 14:32

You don't need to use \left..\right at all, several instances you have do nothing, and others you can specify the sizes via \bigl, \Bigl, \biggl, etc., which do not suffer from problems across line breaks.

Also for a two line split like this multline* is easier.

\documentclass{amsart}

\usepackage{mathtools}

\begin{document}

\begin{multline*}
  \biggl\| (a - c) - \frac{|b|^2\cdot |d|^2}{|b \times d|^2} \biggl[
  \biggl((a - c)\cdot \biggl(\frac{b}{|b|} - \frac{b \cdot
  d}{|b|\cdot|d|} \cdot \frac{d}{|d|}\biggr)\biggr) \cdot \frac{b}{b}
  \\
  + \biggl((a - c)\cdot \biggl(\frac{d}{|d|} - \frac{b \cdot
  d}{|b|\cdot|d|} \cdot \frac{b}{|b|}\biggr)\biggr) \cdot \frac{d}{d}
  \biggr] \biggr\| = \frac{|(a - c) \cdot b \times d|}{|b \times d|}
\end{multline*}

\end{document}

score 1 · Accepted Answer · 2019-04-26T12:47:27.560

Inserting \right.\right. before and \left.\left. seems to help:

\documentclass{article}

\usepackage{mathtools}


\begin{document}

\begin{equation*}
    \begin{aligned}
            \left\| \left(a - c\right) - \frac{|b|^2\cdot |d|^2}{|b \times d|^2} \left[\!\!\!\!\vphantom{\frac{b}{b}}\right.\right.
                                     & \left.\left. \left(\left(a - c\right)\cdot \left(\frac{b}{|b|} - \frac{b \cdot d}{|b|\cdot|d|} \cdot \frac{d}{|d|}\right)\right) \cdot \frac{b}{b} \right.\right. + \\
            & \left.\left. \left(\left(a - c\right)\cdot \left(\frac{d}{|d|} - \frac{b \cdot d}{|b|\cdot|d|} \cdot \frac{b}{|b|}\right)\right) \cdot \frac{d}{d} 
            \right] \right\| = \frac{|(a - c) \cdot b \times d|}{|b \times d|}
    \end{aligned}
\end{equation*}

\end{document}

Cool, you can even delete the ...{split}! – Christoph Apr 26 '19 at 12:40 — Christoph, Apr 26 '19 at 12:40

Error: Extra }, or forgotten \right while keeping the correct hight of brackets

2 Answers2