π |
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3 |
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a |
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π |
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π |
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A.“a=2”是“直线ax+2y=0平行于直线x+y=1”的充分不必要条件 |
B.“x=-1”是“x2-5x-6=0”的必要不充分条件 |
C.命题“若x=y,则sinx=siny”的逆否命题为真命题 |
D.命题“∃x∈R使得x2+x+1<0”的否定是:“∀x∈R,均有x2+x+1<0” |
A.命题“若x2=1,则x=1”的否命题为“若x2=1,则x≠1” | ||||
B.命题“∃x∈R,使得x2+x+1<0”的否定是“∀x∈R,均有x2+x+1<0” | ||||
C.在△ABC中,“A>B”是“cos2A<cos2B”的充要条件 | ||||
D.(x-
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3 |
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1 |
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2 |
1 |
lgx |
a |
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2-x |
2x-1 |
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