# cases environment with material to the left rotated to vertical

Say, I have this MWE:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation*}
\text{ three equations}
\begin{cases}
a &= b + c \\
d &= e + f + g \\
h &= i + j + k + l
\end{cases}
\end{equation*}

\end{document}


What I want is to set the text at the left of the big curly brace to be aligned vertically. I tried:

\documentclass{article}
\usepackage{amsmath}
\usepackage{rotating}

\begin{document}

\begin{equation*}
%\text{ three equations}
\begin{turn}{90}three equations\end{turn}
\begin{cases}
a &= b + c \\
d &= e + f + g \\
h &= i + j + k + l
\end{cases}
\end{equation*}

\end{document}


which aligns the LHS at the middle:

So, the problem is how to adjust the LHS automatically such that is aligned vertically?

• Not solving your question, but I think the &s in the cases environment are useless. – JouleV Dec 18 '18 at 3:29

Use \rotatebox[origin=c]{90} to rotate content about it's centre:

\documentclass{article}

\usepackage{amsmath,makecell}
\usepackage{graphicx}

\begin{document}

$\rotatebox[origin=c]{90}{three equations} \begin{cases} a = b + c \\ d = e + f + g \\ h = i + j + k + l \end{cases} \qquad \rotatebox[origin=c]{90}{\makecell{three \\ equations}} \begin{cases} a = b + c \\ d = e + f + g \\ h = i + j + k + l \end{cases}$

\end{document}