题目内容
已知函数
, 
(Ⅰ)求函数
的定义域;
(Ⅱ)求函数
的单调区间;
(Ⅲ)当
>0时,若存在x使得
成立,求
的取值范围.

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(Ⅰ)求函数

(Ⅱ)求函数

(Ⅲ)当
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
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(1)
;(2)见解析;(3)(0,
.
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本试题主要考查了导数在研究函数中的运用。求解单调区间和不等式的恒成立问题的运用。
解:(Ⅰ)当
时,
;
当
时
(Ⅱ)

(Ⅲ)因为当
时,函数的递增区间为
;单调递减区间为
若存在x使得f(x)
ln2a)成立,只须
,

解:(Ⅰ)当
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
当
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(Ⅱ)

(Ⅲ)因为当


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若存在x使得f(x)
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