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=

2024-11-14 21:05:31
推荐回答(1个)
回答1:

(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)∵

bn
TnTn+1
=
bn+1
qTnTn+1
=
1
q
1
Tn
?
1
Tn+1

b1
T1T2
+
b2
T2T3
+…+
bn
TnTn+1
=
1
q
1
T1
?
1
T2
+
1
T2
?
1
T3
+…+
1
Tn
?
1
Tn+1

=
1
q
1
T1
?
1
Tn+1
)=
1
q
(1-
2
2n+1?1
).