命题:“∀x∈R,都有x2-x+1>0”的否定是( )A.∀x∈R,都有x2-x+1≤0B.∃x∈R,都有x2-x+1>0C.∃x∈R,都有x2-x+1≤0D
题型:不详难度:来源:
命题:“∀x∈R,都有x2-x+1>0”的否定是( )A.∀x∈R,都有x2-x+1≤0 | B.∃x∈R,都有x2-x+1>0 | C.∃x∈R,都有x2-x+1≤0 | D.以上选项均不正确 |
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答案
因为汽车贸易的否定是特称命题, 所以:“∀x∈R,都有x2-x+1>0”的否定是 ∃x∈R,都有x2-x+1≤0. 故选C. |
举一反三
命题“∀x∈R,x2+2x+1>0”的否定是( )A.∀x∈R,x2+2x+1≤0 | B.∃x∈R,x2+2x+1<0 | C.∃x∈R,x2+2x+1>0 | D.∃x∈R,x2+2x+1≤0 |
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已知命题P:∀x>2,x3-8>0,那么¬P是( )A.∀x≤2,x3-8≤0 | B.∃x>2,x3-8≤0 | C.∀x>2,x3-8≤0 | D.∃x≤2,x3-8≤0 |
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