Fuente TeX:

\left\lbrace\begin{matrix} (k-\lambda)a_{11}+(1-k)a_{11} & =0 \\ (k-\lambda) a_{12}+(1-k)a_{21}& =0\\ (k-\lambda) a_{21}+(1-k)a_{12}&=0\\(k-\lambda) a_{22}+(1-k)a_{22}&=0\end{matrix} \right.