a9 |
a5 |
9 |
17 |
S17 |
S9 |
A.1 | B.-1 | C.2 | D.
|
n(a1+an) |
2 |
17(a1+a17) |
2 |
17×2a9 |
2 |
9(a1+a9) |
2 |
9×2a5 |
2 |
a9 |
a5 |
9 |
17 |
S17 |
S9 |
17a9 |
9a5 |
A.20 | B.18 | C.16 | D.12 |
A.
| B.
| C.2 | D.4 |
A.22 | B.33 | C.44 | D.55 |
A.58 | B.88 | C.143 | D.176 |
A.是等比数列但不是等差数列 |
B.是等差数列但不是等比数列 |
C.既是等比数列又是等差数列 |
D.既不是等比数列又不是等差数列 |
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