# Left brace including several lines in eqnarray [duplicate]

How is it possible to make a brace and have something like this in a eqnarray block?

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## marked as duplicate by Werner, Paul Gaborit, T. Verron, barbara beeton, KurtJul 6 '13 at 18:01

Welcome to TeX.SX! You don't have to sign with your name since it automatically appears in the lower right corner of your post. (But you should know this? ;) Could you also add a minimal working example (MWE)?) –  Sean Allred Jul 6 '13 at 16:18
See \eqnarray vs \align on why not to use eqnarray. Then Large braces for specifying values of variables by condition as a possible duplicate, which suggests using cases from amsmath. –  Werner Jul 6 '13 at 16:29

Here's a sample document without the use of amsmath package:

\documentclass{article}
\begin{document}
$\alpha(x)=\left\{ \begin{array}{ll} x\\ \frac{1}{1+e^{-kx}}\\ \frac{e^x-e^{-x}}{e^x+e^{-x}} \end{array} \right.$
\end{document}


or one with amsmath's cases environment

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$\alpha(x)=\begin{cases} x\\ \frac{1}{1+e^{-kx}}\\ \frac{e^x-e^{-x}}{e^x+e^{-x}} \end{cases}$
\end{document}

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