3 |
2 |
1 |
Sn |
13 |
6 |
1 |
2 |
3 |
2 |
3 |
2 |
1 |
2 |
3 |
2n |
| ||||
1+
|
1 |
2 |
1 |
Sn |
1 |
2 |
1 | ||
1-(-
|
1 |
Sn |
1 |
2 |
1 | ||
1+(
|
1 |
2n |
2n |
1+2n |
1 |
2n(2n+1) |
1 |
Sn |
1 |
2 |
1 | ||
1-(
|
1 |
2n(2n-1) |
1 |
Sn |
1 |
Sn |
1 |
S1 |
13 |
6 |
1 |
Sn |
1 |
S2 |
25 |
12 |
1 |
Sn |
13 |
6 |
n | a1a2…an |
A.不是等差数列 | B.是递增数列 |
C.是等差数列 | D.是递减数列 |
A.1或-
| B.1 | C.-
| D.-2 |
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