在等比数列{an}中,a1大于1,公比q大于0,设bn=log以2为底an,且b1+b3+b5=6,b1b3b5=0

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在等比数列{an}中,a1大于1,公比q大于0,设bn=log以2为底an,且b1+b3+b5=6,b1*b3*b5=0.
求{bn}的前n项和Sn及{an}的通项公式an

(1) an=a1q^(n-1)
bn=loga1+(n-1)log(q)为等差数列
(2) b3=6/3=2
b1b5=0
b1=loga1>0
所以b5=0,b1=4
所以bn=5-n
Sn=5n-1/2n^2+1/2n=-1/2n^2+9/2n
an=2^(5-n)

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