# large braces for specifying values of variables by condition

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?

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The »cases« environment from amsmath does the trick.

\documentclass{article}
\usepackage{amsmath}

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

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x = \begin{cases}

amsmath is needed for \text.