S1 |
1 |
S2 |
2 |
Sn |
n |
1 |
2 |
1 |
2 |
n(9-n) |
2 |
n(9-n) |
2 |
Sn |
n |
9-n |
2 |
Sn |
n |
Sn |
n |
Sn |
n |
S1 |
1 |
S2 |
2 |
S3 |
3 |
Sn |
n |
S1 |
1 |
S2 |
2 |
Sn |
n |
A.(-2,0) | B.(2,+∞) | C.(-2,0)∪(2,+∞) | D.(-∞,-2)∪(2,+∞) |
A.-
| B.-
| C.-1<y<1 | D.0<y<2 |
x2+1 |
f(a)+f(b) |
a+b |
A.大于0 | B.小于0 | C.等于0 | D.不确定 |
1 |
2 |
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