http://shicheng.wordpress.com/2009/09/10/latex-formula-in-table/

\section{section}

\begin{tabular}{|c|c|} \hline

Formula & Explanation \\ \hline

      $h_\sigma(a,B)=

            \left\{

            \begin{array}{rl}

                1 & \mbox{if }d(a,B) \leq \sigma  \\

                0 & \mbox{if }d(a,B)> \sigma

            \end{array}\right.

            \label{pan}$

          Explain something here.& your explanation\\ \hline

\end{tabular}