已知
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,若對任意的
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,存在
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,使
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,則實數(shù)m的取值范圍是 ( )
試題分析:由
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,

.所以
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.當(dāng)
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時要使
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成立即要
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存在
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上成立. 存在
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使得
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成立.即

.故選A.本題難點是即有恒成立問題又有存在成立問題.認(rèn)真區(qū)分好這兩個含義是關(guān)鍵.將不等式的問題轉(zhuǎn)化為函數(shù)的最值問題也是解題的關(guān)鍵.
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