Left brace including several lines in eqnarray

Question

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

enter image description here

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 06 '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 06 '13 at 16:29

score 116 · Accepted Answer · edited Jul 15 '17 at 05:15

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}

Left brace including several lines in eqnarray

1 Answers1

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