# Left-align a split equation

I am trying to left-justify a split equation. I would like to have the first line left-justified, and have a hanging indent on the second line. I used flalign successfully for other equations that weren't split, but this split equation is causing me problems. Any suggestions are much appreciated!

\documentclass{article}
\usepackage{amssymb}
\usepackage{amsmath}
\begin{document}
\begin{flalign}
\begin{split}
\Lambda^{12}_{ee}&=\Lambda^{21}_{ee}=\frac{64x_e}{75k_B}\sqrt{\frac{m_e}{2\pi k_BT_e}}\left[\sum_{j\in\set{H}}x_j\left(\frac{175}{16}\Omega^{(1,1)}_{ej}-\frac{315}{8}\Omega^{(1,2)}_{ej}+57\Omega^{(1,3)}_{ej} -30\Omega^{(1,4)}_{ej} \right)\right. \\
&\left.+x_e\sqrt{2}\left(\frac{7}{4}\Omega^{(2,2)}_{ee}-2\Omega^{(2,3)}_{ee}\right)\right]
\end{split}
\end{flalign}

\end{document}

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Welcome to TeX.SX! A tip: If you indent lines by 4 spaces, they'll be marked as a code sample. You can also highlight the code and click the "code" button (with "{}" on it). –  egreg Jun 19 '14 at 14:13
Might also be an idea to post something that actually compiles, what is \set? –  daleif Jun 19 '14 at 14:27

I'm not sure to understand what you mean by “left aligning”; either you left align or center all equations.

For the specific case, the formula is really difficult to split sensibly, so I propose a different strategy:

\documentclass{article}

\usepackage{amsmath}
\usepackage{amssymb}

\newcommand{\set}[1]{#1}%??? The definition was missing

\begin{document}
$$\begin{split} \Lambda^{12}_{ee}&= \Lambda^{21}_{ee}=\frac{64x_e}{75k_B}\sqrt{\frac{m_e}{2\pi k_BT_e}}\, \biggl(\,\sum_{j\in\set{H}}x_jA_{ej}+x_e\sqrt{2}\,B_{e}\biggr)\\ A_{ej}&=\frac{175}{16}\Omega^{(1,1)}_{ej}- \frac{315}{8}\Omega^{(1,2)}_{ej}+ 57\Omega^{(1,3)}_{ej}- 30\Omega^{(1,4)}_{ej} \\[1ex] B_{e}&=\frac{7}{4}\Omega^{(2,2)}_{ee}-2\Omega^{(2,3)}_{ee} \end{split}$$

\end{document}


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If you have the space for it (width) then I'd just use

\documentclass{article}
\usepackage{amssymb}
\usepackage{amsmath}
\let\set\mathbb
\begin{document}
\begin{equation*}
\Lambda^{12}_{ee}=\Lambda^{21}_{ee}=\frac{64x_e}{75k_B}\sqrt{\frac{m_e}{2\pi
k_BT_e}}\biggl[
\!
\begin{aligned}[t]
&\sum_{j\in\set{H}}x_j\left(\frac{175}{16}\Omega^{(1,1)}_{ej}-\frac{315}{8}\Omega^{(1,2)}_{ej}+57\Omega^{(1,3)}_{ej}
-30\Omega^{(1,4)}_{ej} \right)
\\
&+x_e\sqrt{2}\left(\frac{7}{4}\Omega^{(2,2)}_{ee}-2\Omega^{(2,3)}_{ee}\right)\biggr]
\end{aligned}
\end{equation*}

\end{document}

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But @egregs solution is better. –  daleif Jun 19 '14 at 14:30