19.设变量x,y满足约束条件$\left\{\begin{array}{l}{x+y≥3}\\{x-y≥-1}\\{2x-y≤3}\end{array}\right.$,则目标函数z=$\frac{y+1}{x+1}$的最大值为( )
A. | 2 | B. | $\frac{3}{2}$ | C. | $\frac{6}{5}$ | D. | $\frac{2}{3}$ |
18.已知命题p:?x0∈(-∞,0),2${\;}^{{x}_{0}}$<3${\;}^{{x}_{0}}$,命题q:?x∈[-1,1],cosx>$\frac{1}{2}$,则下列命题为真命题的是( )
A. | p∧q | B. | p∨(¬q) | C. | (¬p)∧q | D. | p∧(¬q) |
14.过点A(0,2),B(-2,2),且圆心在直线x-y-2=0上的圆的方程是( )
A. | (x-1)2+(y+1)2=26 | B. | (x+1)2+(y+3)2=26 | C. | (x+2)2+(y+4)2=26 | D. | (x-2)2+y2=26 |
13.若两平行线3x+4y-4=0与ax+4y+b=0(b>0)间的距离是2,则a+b等于( )
A. | 9 | B. | -18 | C. | 2 | D. | 10 |
12.若直线ax+(2a-3)y=0的倾斜角为45°,则a等于( )
A. | 2 | B. | -2 | C. | 1 | D. | -1 |
10.f(x)定义在(0,+∞)上的非负可导函数,且满足xf′(x)+f(x)≤0,对任意的正数a,b,若a<b,则必有( )
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A. | bf(b)≤af(a) | B. | bf(a)≤af(b) | C. | af(a)≤bf(b) | D. | af(b)≤bf(a) |