Sn |
Tn |
7n+1 |
4n+27 |
A.4:3 | B.3:2 | C.7:4 | D.78:71 |
22(a1+a21) |
2 |
22(b1+b21) |
2 |
S21 |
T21 |
21a11 |
21b11 |
a11 |
b11 |
7×21+1 |
4×21+27 |
4 |
3 |
a | 2n |
sn |
(n+50)sn+1 |
n(an+1) |
2 |
1 |
(2an+1)(2an-1) |
k |
57 |
A.130 | B.170 | C.210 | D.260 |
A.若n≥2且an+1+an-1=2an,则{an}是等差数列 |
B.设数列{an}的前n项和为Sn,且2Sn=1+an,则数列{an}的通项an=(-1)n-1 |
C.若n≥2且an+1an-1=an2,则{an}是等比数列 |
D.若{an}是等比数列,且m,n,k∈N+,m+n=2k,则aman=ak2 |
Sn |
an-3 |
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