若存在行列式:
则(|A|)具有以下性质:
性质1的证明:
由矩阵转置相关性质可知:
[(a_{ij})^T=a(_{ji})\ ]
而:
[|A|=sum (-1)^ta_{1p_1}cdot a_{2p_2}cdot a_{3p_3}...cdot a_{np_n}\ |A|^T=sum (-1)^ta_{p_11}cdot a_{p_22}cdot a_{p_33}cdot ... a_{p_nn} ]
故:
[tag{1}|A|^T=|A| ]
性质2的证明:
若(|A|=sum (-1)^ta_{1p_1}cdot a_{2p_2}cdot a_{3p_3}...a_{jp_j}...a_{kp_k}...cdot a_{np_n})
设将|A|中第(j)行和第(k)行进行互换形成的行列式为(|A^{kj}|):
相对(|A|)而言,(|A^{kj}|)中的全排列变为:(p_1p_2p_3...p_k...p_j...p_n),即产生(或减少)了1个逆序数:
[\ Rightarrow |A^{kj}|=sum (-1)^{tpm1}a_{1p_1}cdot a_{2p_2}cdot a_{3p_3}...a_{kp_k}...a_{jp_j}...cdot a_{np_n}\ ]
[Rightarrowtag{2} |A^{kj}|=-|A| ]
性质3的证明:
根据性质2可知:(|A^{kj}|=-|A|)
若(|A|)中(k,j)两行的值完全相同,则:
[|A^{kj}|=|A|\ Rightarrow |A| =-|A| ]
[Rightarrowtag{3} |A| = 0 ]
性质4的证明:
由(|A|=sum (-1)^ta_{1p_1}cdot a_{2p_2}cdot a_{3p_3}...cdot a_{np_n})可知:
[lambda cdot |A|=sum (-1)^t cdot lambda cdot a_{1p_1}cdot a_{2p_2}cdot a_{3p_3}...cdot a_{np_n} ]
由性质1可知:(|A|=|A|^T)
[Rightarrow lambda cdot |A|=lambda cdot |A|^T=sum (-1)^ta_{p_11}cdot a_{p_22}cdot a_{p_33}cdot ... a_{p_nn} ]
又知(p_1p_2p_3......p_n) 是|A|中的全排列,故(a_{ip_i})表示第i行任一元素,(a_{p_ii})表示第i列任一元素(i=1,2,3...,n),则:
[lambda cdot |A|=sum (-1)^t cdot (lambda cdot a_{1p_1})cdot a_{2p_2}cdot a_{3p_3}...cdot a_{np_n}\ qquadquad=sum (-1)^t cdot a_{1p_1}cdot a_{2p_2}cdot a_{3p_3}...cdot (lambda cdot a_{np_n})\ ]
[qquadquadquadquad=lambda cdot |A|^T=sum (-1)^t(lambda cdot a_{p_11})cdot a_{p_22}cdot a_{p_33}cdot ... a_{p_nn}\ qquadquadquadquad......\ qquadquadquadquad=lambda cdot |A|^T=sum (-1)^ta_{p_11}cdot a_{p_22}cdot a_{p_33}cdot ... (lambda cdot a_{p_nn})\ qquadquadquadquad...... ]
[Rightarrow lambda cdot |A|= begin{vmatrix} lambda cdot a_{11} & lambda cdot a_{12} & lambda cdot a_{13} &...& lambda cdot a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix}\ ]
[tag{4}qquadqquad= begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ lambda cdot a_{n1} & lambda cdot a_{n2} & lambda cdot a_{n3} &...& lambda cdot a_{nn}\ end{vmatrix} ]
[=lambda cdot|A|^T= begin{vmatrix} lambda cdot a_{11} & a_{12} & a_{13} &...& a_{1n}\ lambda cdot a_{21} & a_{22} & a_{23} &...& a_{2n}\ lambda cdot a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ lambda cdot a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix}\ ]
[...... ]
[tag{5} qquadqquad = begin{vmatrix} a_{11} & a_{12} & a_{13} &...& lambda cdot a_{1n}\ a_{21} & a_{22} & a_{23} &...& lambda cdot a_{2n}\ a_{31} & a_{32} & a_{33} &...& lambda cdot a_{3n}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& lambda cdot a_{nn}\ end{vmatrix} ]
设(|A|)存在第(x)行:
[|A|= begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{x1} & a_{x2} & a_{x3} &...& a_{xn}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix}\ ]
若(|A|)中满足:(a_{1i}=lambda cdot a_{xi}(i=1,2,3,...,n)),则(|A|)可写为如下形式:
[|A|= begin{vmatrix} lambda cdot a_{x1} & lambda cdot a_{x2} & lambda cdot a_{x3} &...& lambda cdot a_{xn}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{x1} & a_{x2} & a_{x3} &...& a_{xn}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix}\ ]
[=lambda cdot begin{vmatrix} a_{x1} & a_{x2} & a_{x3} &...& a_{xn}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{x1} & a_{x2} & a_{x3} &...& a_{xn}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix} ]
则根据性质4,可得:
[lambda cdot begin{vmatrix} a_{x1} & a_{x2} & a_{x3} &...& a_{xn}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{x1} & a_{x2} & a_{x3} &...& a_{xn}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix}=lambda cdot0=0 qquad qquad qquad(6) \ ]
设(|A|)存在第(z)行:
[|A|= begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{z1} & a_{z2} & a_{z3} &...& a_{zn}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix}\ ]
若第z行元素均满足:(a_{z_i}=a_{x_i}+a_{y_i};(i=1,2,3,...,n))
则:
[|A|=sum(-1)^ta_{1p_1} cdot a_{2p_2} cdot ... cdot a_{zp_z}cdot ... cdot a_{np_n}\ qquad qquad quad=sum(-1)^ta_{1p_1} cdot a_{2p_2} cdot ... cdot (a_{xp_x}+a_{yp_y})cdot ... cdot a_{np_n}\ qquad qquad quad=sum(-1)^ta_{1p_1} cdot a_{2p_2} cdot ... cdot a_{xp_x}cdot ... cdot a_{np_n}+sum(-1)^ta_{1p_1} cdot a_{2p_2} cdot ... cdot a_{yp_y}cdot ... cdot a_{np_n}\ ]
则(|A|)可具有以下性质:
[|A|= tag{7} begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{z1} & a_{z2} & a_{z3} &...& a_{zn}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix}\ =begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{x1} & a_{x2} & a_{x3} &...& a_{xn}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix} +begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3n}\ & & ......\ a_{y1} & a_{y2} & a_{y3} &...& a_{yn}\ & & ......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nn}\ end{vmatrix} ]
同理,可通过性质1证得以下性质(过程略):
[begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1z} & ... & a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2z} & ... & a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3z} & ... & a_{3n}\ & & &......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nz} & ... & a_{nn}\ end{vmatrix}\ =begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1x} & ... & a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2x} & ... & a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3x} & ... & a_{3n}\ & & &......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nx} & ... & a_{nn}\ end{vmatrix} +begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1y} & ... & a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2y} & ... & a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3y} & ... & a_{3n}\ & & &......\ a_{n1} & a_{n2} & a_{n3} &...& a_{ny} & ... & a_{nn}\ end{vmatrix} ]
设行列式|A|中存在第x列、第y列:
[|A|= begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1x} & ... & a_{1y} & ... & a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2x} & ... & a_{2y} & ... & a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3x} & ... & a_{3y} & ... & a_{3n}\ & & &......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nx} & ... & a_{ny} & ... & a_{nn}\ end{vmatrix} ]
若使第x列的数值产生以下变化,则|A|的值保持不变:
[tag {8} 由a_{ix}变为(a_{ix}+lambda cdot a_{iy})quad(i=1,2,3,...,n) ]
则新生成的行列式(|A|')为:
[|A|'= begin{vmatrix} a_{11} & a_{12} & a_{13} &...& (a_{1x}+lambda cdot a_{1y}) & ... & a_{1y} & ... & a_{1n}\ a_{21} & a_{22} & a_{23} &...& (a_{2x}+lambda cdot a_{2y}) & ... & a_{2y} & ... & a_{2n}\ a_{31} & a_{32} & a_{33} &...& (a_{3x}+lambda cdot a_{3y}) & ... & a_{3y} & ... & a_{3n}\ & & &......\ a_{n1} & a_{n2} & a_{n3} &...& (a_{nx}+lambda cdot a_{ny}) & ... & a_{ny} & ... & a_{nn}\ end{vmatrix} ]
根据性质6可得:
[|A|'= begin{vmatrix} a_{11} & a_{12} & a_{13} &...& a_{1x} & ... & a_{1y} & ... & a_{1n}\ a_{21} & a_{22} & a_{23} &...& a_{2x} & ... & a_{2y} & ... & a_{2n}\ a_{31} & a_{32} & a_{33} &...& a_{3x} & ... & a_{3y} & ... & a_{3n}\ & & &......\ a_{n1} & a_{n2} & a_{n3} &...& a_{nx} & ... & a_{ny} & ... & a_{nn}\ end{vmatrix}\ + begin{vmatrix} a_{11} & a_{12} & a_{13} &...& lambda cdot a_{1y} & ... & a_{1y} & ... & a_{1n}\ a_{21} & a_{22} & a_{23} &...& lambda cdot a_{2y} & ... & a_{2y} & ... & a_{2n}\ a_{31} & a_{32} & a_{33} &...& lambda cdot a_{3y} & ... & a_{3y} & ... & a_{3n}\ & & &......\ a_{n1} & a_{n2} & a_{n3} &...& lambda cdot a_{ny} & ... & a_{ny} & ... & a_{nn}\ end{vmatrix} ]
[Rightarrow |A|'=|A|+0=|A| ]
同理,设行列式|A|中存在第x行、第y行,若使x行产生以下变化,则|A|的值保持不变:
[tag{9} 由a_{xj}变为(a_{xi}+lambda cdot a_{yi})quad(i=1,2,3,...,n) ]
(证明过程参考后续知识点)
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