当4≠0时, 141+a1242+…+an4n=4 +an242+…+amAm=|A当A  0时,                             =  n n nn n n n n nn n n A A A A A A A A A a a a a a a a a a AA               1 2 1 2 2 2 2 1 1 2 1 1 1 2 2 1 2 2 2 1 1 1 2 1 a11A11 + a12A12 ++ a1nA1n = A an1An1 + an2An2 ++ annAnn = A ,               = A A A A O O 