12.矩阵的秩及相关性质12.1k阶子式12.1.1k阶子式示例设存在以下矩阵：\[X_{mn}=\begin{bmatrix}x_{11}&x_{12}&x_{13}&...&x_{1n}\\x_{21}&x_{22}&x_{23}&...&x_{2n}\\x_{31}&x_{32}&x_{33}&...&x_{3n}\\&