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=5(T3+b2). (Ⅰ)求数列{an},{bn}的通项公式; (Ⅱ)求和:b1T1T2+b2T2T3+
问题描述:
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=5(T3+b2).
(Ⅰ)求数列{an},{bn}的通项公式;
(Ⅱ)求和:
+b1
T1T2
+…+b2
T2T3
. bn
TnTn+1
答
(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)∴...