# 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?

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

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}