当4≠0时, 41+a12412+…+an4,n=4 n14n1+n2n2+…+a.4 A A 上页当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