命题“∀x∈R,x2+x>0”的否定是“ .
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的图象C上存在一个定点P满足:若过定点P的直线l与曲线C交于不同于P的两点M(x
1,y
1),N(x
2,y
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A.-
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B.
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C.
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D.-2
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已知x,y满足
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,且目标函数z=-x+2y的最大值为5,最小值为-1,则
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