Cases

\documentclass{article}


\usepackage{amsmath}

\title{Cases}
\author{VK}
\date{\today}

\begin{document}

\maketitle

$$
1+(-1)^n=\begin{cases}
			0, & \text{if $n$ odd}\\
            2, & \text{otherwise}
		 \end{cases}
$$

\end{document}