# Problem with breaking line in align mode [duplicate]

Here is the issue and here is the code.

\begin{align*}
\left ( \frac{1+\sqrt{3}}{2\sqrt{2}}+ i \frac{\sqrt{3}-1}{2\sqrt{2}} \right )^{72} &=  \left [ \left ( \frac{1}{2}\cdot \frac{\sqrt{2}}{2}+ \frac{\sqrt{3}}{2}\cdot \frac{\sqrt{2}}{2} \right )+ i \left ( \frac{\sqrt{3}}{2}\cdot \frac{\sqrt{2}}{2} -\frac{1}{2}\frac{\sqrt{2}}{2} \right ) \right ]^{72}\\
&=\left [ \left ( \cos \frac{\pi}{3}\cos \frac{\pi}{4} + \sin \frac{\pi}{3}\sin \frac{\pi}{4} \right ) +i \left ( \sin \frac{\pi}{3} \cos \frac{\pi}{4} - \cos \frac{\pi}{3} \sin \frac{\pi}{4}  \right ) \right ]^{72} \\
&= \left [ \cos \left ( \frac{\pi}{3} - \frac{\pi}{4} \right ) +i \sin \left ( \frac{\pi}{3} - \frac{\pi}{4} \right )\right ]^{72}\\
&= \left ( \cos \frac{\pi}{12} + i \sin \frac{\pi}{12} \right )^{72}\\
&= \left ( \cos^2 \frac{\pi}{12} - \sin^2 \frac{\pi}{12} +2i \cos \frac{\pi}{12} \sin \frac{\pi}{12} \right )^{36}\\
&=\left ( \cos \frac{\pi}{6} + i \sin \frac{\pi}{6} \right )^{36} \\
&= \left ( \frac{\sqrt{3}}{2}+\frac{i}{2} \right )^{36} \\
&=\left [ \left ( \frac{\sqrt{3}}{2}+ \frac{i}{2} \right )^3 \right ]^{12} \\
&=1
\end{align*}


The line

\left [ \left ( \cos \frac{\pi}{3}\cos \frac{\pi}{4} + \sin \frac{\pi}{3}\sin \frac{\pi}{4} \right ) +i \left ( \sin \frac{\pi}{3} \cos \frac{\pi}{4} - \cos \frac{\pi}{3} \sin \frac{\pi}{4}  \right ) \right ]^{72}


however exceeds the margins of the page so I want to break it. I used \\ and then on the new line & plus two \qquad to bring it in a favor position and altough it gets a result the compile ends up with errors which is something logical. The output is that the final ] in that line is not depicted at all.

How can I break up that line? Need I use alignat package?

• Try with \bigg[ and \bigg] instead of \left[ and \right]. Should produce what you want. There's also \big[ \big] if you want slightly smaller brackets.
– user49901
Mar 14, 2016 at 11:03
• @Grimler \biggl[ and \biggr] to get correct open and close spacing. Mar 14, 2016 at 11:06
• @DavidCarlisle I really admire some people that give a link here to a possible duplicate. I searched and searched but in vain. Thanks. Mar 14, 2016 at 11:06
• @Grimler and David Carlisle ... Thank you both. I guess what David suggests is a little better. I'll adopt that one. Mar 14, 2016 at 11:07
• @Tolaso usually it is easier to search for the answer than search for the question, but then if you can do that you don't need to ask:-) Mar 14, 2016 at 11:08

\biggl[ ... \biggr]

so that we have a better open and close spacing. Then at the point we are breaking the line we insert \\ and the new line we also insert & so that we have the alignment and if necessary some space commands e.g \quad , \qquad or whatever so that the new expression comes to a favor position.