# Tagging several groups of equations in the same environment

I have long equations, so I have to break them with this structure:

something = long expression1
continuation of long expression1
= long expression2
continuation of long expression2
= etc


What I want to do is to group the first two lines corresponding to expression1 and tag them together. I do this via

\begin{equation}
\begin{aligned}
something = long expression1
continuation of long expression1
\end{aligned}
\end{equation}


This will correctly put a tag in-between the two lines. I want to add to the environment equation the other expressions (i.e. expression2, expression3, etc.): This is what I attempted:

\begin{equation}
\begin{aligned}
\Kam =& -\frac{1}{m}\left[\frac{q^2B^2}{4c^2}(\sqrt{2P_1}\cos Q_1 - Q_2)^2 + \frac{q^2B^2}{4c^2}(\sqrt{2P_1}\sin Q_1 - P_2)^2\right]\\
&+\frac{B^2q^2}{8mc^2}\left[\frac{c^2}{q^2B^2}(\sqrt{2P_1}\sin Q_1 + P_2)^2 + \frac{c^2}{q^2B^2}(\sqrt{2P_1}\cos Q_1 + Q_2)^2\right]\\
&+\frac{Bq}{2mc}\left[\frac{1}{\alpha}(\sqrt{2p_1}\cos Q_1 + Q_2)\frac{\alpha}{2}(\sqrt{2P_1}\cos Q_1 - Q_2) \right.\\
&\phantom{+\frac{Bq}{2mc}\left[\right.\,\,} + \left.\frac{1}{\alpha}(\sqrt{2P_1}\sin Q_1 + P_2)\frac{\alpha}{2}(\sqrt{2P_1}\sin Q_1 - P_2)\right]
\end{aligned}\\
\begin{aligned}
This is my second expression
\end{aligned}
\end{equation}


But repeating aligned does not work: • Just repeated aligned as many time as you wish :-) of course, not in equation environment but in align or gather. – Zarko Mar 20 '16 at 14:25
• @Zarko can you write this as an answer? So that the answer does not remain unanswered. Also, how do I align the equal symbols in different aligned environments? – Vladimir Vargas Mar 20 '16 at 14:29
• How is the macro \Kam defined? – Mico Mar 20 '16 at 15:19

## 1 Answer

I need some time to figured out your equation, it is huge and wider than text width, so I give up with its simulation ...). With simplifying your equation I obtain the following result: \documentclass[border=3mm,
preview]{standalone}
\usepackage{mathtools}

\begin{document}
\begin{align}
\begin{split}
Kam & = \text{This is first line  of my first expression}\\
&\qquad + \text{This is second line of my first expression}\\
&\qquad + \text{This is third line of my first expression}
\end{split}\\
\begin{split}
& = \text{This is my second expression}
\end{split}
\end{align}
\end{document}


Main difference is that instead of equation I use align environment. If you more like to use aligned environment instead of split, just replace it accordingly. You will obtain the same result.