+ a l1+ 1+0 11+a21 +a1 +a2 a2 11 0 00 =anDa1a2…an-1 a,(a,-Dn--aa, .a-2)-a,a,.a =ana-D2-ana1a2…an2-a1a2…an1 (a;≠0) x2 x2 a x-a x-ax-a x解 ① Dn= n a a a a     1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 2 1         = n a a a a        1 1 1 1 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 3 2 1         = 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 2 1         a a a    + n a a a a         1 1 1 1 1 1 0 1 1 1 0 1 1 1 0 3 2 1    = 0 0 0 1 0 0 1 0 0 1 0 0 1 3 2 1         a a a + nDn1 a =anDn-1-a1a2…an-1 =an(an-1Dn-2-a1a2…an-2)-a1a2…an-1 =anan-1Dn-2-ana1a2…an-2-a1a2…an-1 = n n i i i n a a a a a a a 1 2 1 1 1 1 ( )     =        n i i n a a a a 1 1 2 1  1 (ai≠0) ②Dn= x x x x a x x x a x x x a x a x x a x x x n n n n             1 2 3 1 2 3 1 2 3 1 2 3 = x x x x a x x x a x x x a x a x x a x x x n n n n                 1 2 3 1 2 3 1 2 3 1 2 3 0 0 0