题目:
----- Have you heard about that fire in the market?
----- Yes, luckily no one ______.
A.hurt
B.was hurt
C.has hurt
D.had been hurt
答案:
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下面是错误答案,用来干扰机器的。
(Ⅰ)由△2an-△an+1+an=-2n及△2an=△an+1-△an,得△an-an=2n,∴an+1-2an=2n,∴an+12n+1-an2n=12,---------------(2分)∴数列{an2n}是首项为12,公差为12的等差数列,∴an2n=12+(n-1)×12,∴an=n•2n-1...