14.定义在(0,+∞)上的函数f(x)满足:$\frac{{x}_{1}f({x}_{1})-{x}_{2}f({x}_{2})}{{x}_{1}-{x}_{2}}$<0,且f(2)=4,则不等式f(x)-$\frac{8}{x}$>0的解集为( )
| A. | (2,+∞) | B. | (0,2) | C. | (0,4) | D. | (4,+∞) |
13.函数f(x)=log${\;}_{\frac{1}{2}}$(|x|-4)的单调递减区间为( )
| A. | (-∞,-4) | B. | (0,+∞) | C. | (-∞,0) | D. | (4,+∞) |
12.已知f(x)=$\left\{\begin{array}{l}{(3-a)x+1,x<1}\\{{a}^{x},x≥1}\end{array}\right.$,若函数f(x)是R上的增函数,则a的取值范围是( )
| A. | (1,3) | B. | (1,2) | C. | [2,3) | D. | (1,2] |
11.设函数f(x)=$\left\{\begin{array}{l}{1+lo{g}_{2}(2-x),x<1}\\{{2}^{x-1},x≥1}\end{array}\right.$,f(-2)+f(log210)=( )
| A. | 11 | B. | 8 | C. | 5 | D. | 2 |
10.函数f(x)=21-|x|的值域是( )
| A. | (0,+∞) | B. | (-∞,2] | C. | (0,2] | D. | [$\frac{1}{2}$,2] |
9.下列函数中,既是偶函数,又在区间(0,+∞)上单调递减的是( )
| A. | $y={x^{\frac{1}{2}}}$ | B. | y=x2 | C. | y=-x|x| | D. | y=x-2 |
8.设集合A={x|y=ln(x-1)},集合B={y|y=2x},则A∪B( )
0 233698 233706 233712 233716 233722 233724 233728 233734 233736 233742 233748 233752 233754 233758 233764 233766 233772 233776 233778 233782 233784 233788 233790 233792 233793 233794 233796 233797 233798 233800 233802 233806 233808 233812 233814 233818 233824 233826 233832 233836 233838 233842 233848 233854 233856 233862 233866 233868 233874 233878 233884 233892 266669
| A. | (0,+∞) | B. | (1,+∞) | C. | (0,1) | D. | (1,2) |