Fuente TeX:

\begin{pmatrix}a_{1}&a_{2}\\a_{3}&a_{4}\end{pmatrix} = \alpha_1 \begin{pmatrix}1&0\\0&1\end{pmatrix} + \alpha_2 \begin{pmatrix}0&1\\1&0\end{pmatrix} + \alpha_3 \begin{pmatrix}-1&0\\0&1\end{pmatrix} + \alpha_4 \begin{pmatrix}0&1\\-1&0\end{pmatrix}