Para escribir determinantes y matrices en LaTex utilizaremos el entorno array.
\left|
\begin{ array}{cc}
H_{11}-WS_{11} & H_{12}-WS_{12}\\
H_{21}-WS_{21} & H_{22}-WS_{22}
\end{array}
\right|=0
El resusltado es el siguiente:
$$\left| \begin{array}{cc} H_{11}-WS_{11} & H_{12}-WS_{12}\\ H_{21}-WS_{21} & H_{22}-WS_{22} \end{array} \right|=0$$