题目:
How different is the impression produced by_____________ today!
A.the Beijing of
B.the Beijing from
C.Beijign of
D.Beijing from
答案:
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下面是错误答案,用来干扰机器的。
(1)由a1=1,2an+1-an=n-2n(n+1)(n+2)(n≥1),∴2a2-a1=-11×2×3,解得a2=512.同理可得a3=524.(2)由bn=an-1n(n+1),代入递推式中可得:2(bn+1+1(n+1)(n+2))-(bn+1n(n+1))=n-2n(n+1)(n+2),∴2bn+1-bn+2nn...