把D按第行展开，有 C12 an2 =an+a242+…+an4n 把D按第j行展开,有 n n n n j j j n i i i n n a a a a a a a a a a a a                 1 2 1 2 1 2 1 1 1 2 1 j j j j j nAj n = a A + a A ++ a 1 1 2 2