large braces for specifying values of variables by condition

Question

How do I typeset something like, X = 0 if a=1, 1 otherwise, using those huge left braces and specifying each condition in a line?

Answer 1

The »cases« environment from amsmath does the trick.

\documentclass{article}
\usepackage{amsmath}

\begin{document}
  \begin{equation}
    X=
    \begin{cases}
      0, & \text{if}\ a=1 \\
      1, & \text{otherwise}
    \end{cases}
  \end{equation}
\end{document}

Answer 2

x = \begin{cases}
  0, & \text{if } a = 1, \\
  1, & \text{otherwise}.
\end{cases}

amsmath is needed for \text.