.已知命题
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:存在
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;命题
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:
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中,若
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,则
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,则下列命题中为真命题的是( )
本题考查复合命题的真假判定。
解答:对于命题
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,当
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时,
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故是假命题。
对于命题
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在
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中,当
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时,若
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都为锐角,则
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,
当
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有一个为钝角,不妨设为
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,由
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,则
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,即
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也满足
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,故为真命题。所以
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且
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假命题,
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或
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假命题,
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且
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真命题,
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且
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假命题,故选C。
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
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
.
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