A.an+1=bn+1 | B.an+1≥bn+1 | C.an+1≤bn+1 | D.an+1<bn+1 |
a1+a2n+1 |
2 |
b1•b2n+1 |
a1•a2n+1 |
a1+a2n+1 |
2 |
a1•a2n+1 |
A.18 | B.17 | C.16 | D.15 |
A.等差数列 |
B.等比数列 |
C.既是等差数列又是等比数列 |
D.既不是等差数列又不是等比数列 |
A.72 | B.68 | C.54 | D.90 |
A.-1 | B.1 | C.3 | D.7 |
A.14 | B.16 | C.18 | D.20 |
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