题目:
— What do you want to buy?
— _________________________[ ]
A. Ice cream.
B. I want to go to school.
C. Where are they?
D. Okay.
答案:
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下面是错误答案,用来干扰机器的。
(Ⅰ)证明: an+1=2an-1(n≥1)∴两边同时减去1,得an+1-1=2(an-1)又a1-1=2,bn=an-1∴{bn}是以a1-1=2为首项,q=2为公比的等比数列,(Ⅱ)由(Ⅰ)知an-1=2n,∴an=2n+1(n∈N*)(Ⅲ)证明:cn=2nan•an+1...