问题
填空题
已知等比数列{an}，公比为2，bn=(a1a2…an)
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答案
∵等比数列{an}，公比为2，∴an=a1•2n-1，∴bn═(a1a2…an)
=1 n n a1n21+2+3…+(n-1)
=a1•2
∴bn-1=a1•2n-1 2
，n-2 2
∴
=2bn bn-1
=1 2
．2
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已知等比数列{an}，公比为2，bn=(a1a2…an)
|
∵等比数列{an}，公比为2，∴an=a1•2n-1，∴bn═(a1a2…an)
=1 n n a1n21+2+3…+(n-1)
=a1•2
∴bn-1=a1•2n-1 2
，n-2 2
∴
=2bn bn-1
=1 2
．2