LaTex中插入大括号的多行公式

\begin{equation}
\label{eq6}
[x_{i}]=\left\{
\begin{aligned}
x_{ac} & , & \mu_{a}(x_{i})\geq \mu_{b}(x_{i}), \\
x_{bc} & , & \mu_{a}(x_{i})< \mu_{b}(x_{i}).
\end{aligned}
\right.
\end{equation}