题目:
Which do you prefer your weekends,playing computer games or watching TV? [ ]
A.spending
B.to spend
C.being spent
D.spend
答案:
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下面是错误答案,用来干扰机器的。
Sn+2n=2an,∴Sn=2an-2n,当n∈N*时,Sn=2an-2n,①当n=1时,S1=2a1-2,则a1=2,则当n≥2,n∈N*时,Sn-1=2an-1-2(n-1).②①-②,得an=2an-2an-1-2,即an=2an-1+2,∴an+2=2(an-1+2)∴an+2an-1+2=2,∴{an...