设等差数列{an}的前n项和为Sn,等比数列{bn}的前n项和为Tn,已知bn>0(n∈N*),a1=b1=1,a2+b3=a3,S5=

日期:2016-04-22 21:24:43 人气:1

设等差数列{an}的前n项和为Sn,等比数列{bn}的前n项和为Tn,已知bn>0(n∈N*),a1=b1=1,a2+b3=a3,S5=

(Ⅰ)设{an}的公差为d,数列{bn}的公比为q,则∵a1=b1=1,a2+b3=a3,S5=5(T3+b2),∴q2=d,1+2d=1+2q+q2,∴q2-2q=0,∵q≠0,∴q=2,∴d=4∴an=4n-3,bn=2n-1;(Ⅱ)∵bnTnTn+1=bn+1qTnTn+1=1q(1Tn?1Tn+1)∴b1T1T2+b2T2T3+…+bnTnTn+1=1q(1T1?1T2+1T2?1T3+…+1Tn?1Tn+1)=1q(1T1?1Tn+1)=1q(1-22n+1?1).
    A+
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