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已知实数x,y满足不等式组,若目标函数z=y-ax取得最大值时的唯一最优解是(1...
已知实数x,y满足不等式组
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,若目标函数z=y-ax取得最大值时的唯一最优解是(1,3),则实数a的取值范围为( )
A.a<-l
B.0<a<l
C.a≥l
D.a>1
考点分析:
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有下列四个命题:
p
1:∃x,y∈R,sin(x-y)=sinx-siny;
p
2:已知a>0,b>0,若a+b=1,则
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的最大值是9;
p
3:直线ax+y+2a-1=0过定点(0,-l);
p
4:区间
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是
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的一个单调区间.
其中真命题是( )
A.p
1,p
4B.p
2,p
3C.p
2,p
4D.p
3,p
4
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若a,b为实数,则“0<ab<1”是“
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”的( )
A.充分而不必要条件
B.必要而不充分条件
C.充分必要条件
D.既不充分也不必要条件
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已知圆x
2+y
2+mx-
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=0与抛物线y=
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的准线相切,则m的值等于( )
A.±
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B.
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C.
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D.±
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具有如图所示的正视图和俯视图的几何体中,体积最大的几何体的表面积为( )
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A.13
B.7+3
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C.
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D.14
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在△ABC中,角A,B,C所对的边分别为a,b,c,若
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,则角B为( )
A.
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B.
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C.
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D.
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