问题
选择题
设正数a，b满足
|
答案
∵
(x2+ax-b)=4⇒4+2a-b=4⇒2a=b，lim x→2
∴
=a b
．1 2
∴lim n→∞
=an+1+abn-1 an-1+2bn lim n→∞
=a(
)n+a b a b
(1 a
)n+2a b lim n→∞
=a(
)n+1 2 1 2
(1 a
)n+21 2
.1 4
故选B．
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