用 Laplace 定理计算
$D=\left|\begin{array}{cccccc}a_{11} & \cdots & a_{1 n} & 0 & \cdots & 0 \\ \vdots & & \vdots & \vdots & & \vdots \\ a_{n 1} & \cdots & a_{n n} & 0 & \cdots & 0 \\ c_{11} & \cdots & c_{1 n} & b_{11} & \cdots & b_{1 m} \\ \vdots & & \vdots & \vdots & & \vdots \\ c_{m 1} & \cdots & c_{m n} & b_{m 1} & \cdots & b_{m m}\end{array}\right|$ ；