# How can I align multiple cases environment simultaneously?

In one big align environment, I want to put some cases environments. I would like the alignment of the cases environments to be the same. For example, if I write:

\begin{align}
f(x) &=
\begin{cases}
x & \text{if } x\geq 0,\\
-x & \text{if } x <0,
\end{cases}\\
g(x) &=
\begin{cases}
\sqrt{x} & \text{if } x \geq 0,\\
-\sqrt{-x} & \text{if } x < 0.
\end{cases}
\end{align}


then the equation looks ugly because the two cases environment are aligned at different points. Is there a way to force the alignment point of the two environment to be the same?

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See also Aligning the right parts in multiple \begin{cases} (possible duplicate), but here you have the better answers. –  Hendrik Vogt Feb 3 '13 at 8:09
I searched for it, but I did not find anything. Thanks! –  antonio Feb 4 '13 at 17:12

You could also use a \hphantom{} to add the appropriate amount of horizontal space:

## Code:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
f(x) &=
\begin{cases}
x\hphantom{-\sqrt{-}} & \text{if } x\geq 0,\\
-x & \text{if } x <0,
\end{cases}\\
g(x) &=
\begin{cases}
\sqrt{x} & \text{if } x \geq 0,\\
-\sqrt{-x} & \text{if } x < 0.
\end{cases}
\end{align}
\end{document}

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I was hoping in something that does not require some sort of manual spacing, that I could also use in more complicated examples. Thank you anyway! –  antonio Feb 4 '13 at 17:16

You can enclose one of the entries in the first cases environment in a box whose width is that of the longest of the second cases environment.

\newlength{\temp}
\settowidth{\temp}{$-\sqrt{-x}$}
\begin{align}
f(x) &=
\begin{cases}
\makebox[\temp][l]{$x$} & \text{if } x\geq 0,\\
-x & \text{if } x <0,
\end{cases}\\
g(x) &=
\begin{cases}
\sqrt{x} & \text{if } x \geq 0,\\
-\sqrt{-x} & \text{if } x < 0.
\end{cases}
\end{align}


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