证：aa12ain......D=ai+0+..+0 0+ai2 +..+0 .. 0+...+0+ain...·anian2ann..auauainailayra12a12福n1++dinaannanlan2anQ....0an2= ai,Ai + aizA2 +... + ainAin(i = 1,2,..,n)Rs2.6行列式按一行（列）展开§2.6 行列式按一行（列）展开 证： 11 12 1 1 2 1 2 0 0 0 0 0 0 n i i in n n nn a a a D a a a a a a = + + + + + + + + + i i i i in in 1 1 2 2 = + + + a A a A a A 11 12 1 11 12 1 11 12 1 1 2 1 2 1 2 1 2 0 0 0 0 0 0 n n n i i in n n nn n n nn n n nn a a a a a a a a a a a a a a a a a a a a a = + + + (i = 1,2,  ,n)