2.若函数f(x)=x+$\frac{b}{x}$(b∈R)的导函数在区间(1,2)上有零点,则f(x)在下列区间上单调递增的是( )
| A. | (-∞,-1] | B. | (-1,0) | C. | (0,1) | D. | (2,+∞) |
20.已知函数f(x)是定义在R上的奇函数,当x≥0时f(x)=$\frac{1}{2}$(|x-a|+|x-2a|-3a),若?x∈R,f(x-1)≤f(x),则正数a的取值范围为( )
| A. | (0,$\frac{1}{36}$] | B. | (0,$\frac{1}{9}$] | C. | (0,$\frac{1}{6}$] | D. | (0,$\frac{1}{3}$] |
18.下列函数中,值域为(0,+∞)的函数是( )
0 233728 233736 233742 233746 233752 233754 233758 233764 233766 233772 233778 233782 233784 233788 233794 233796 233802 233806 233808 233812 233814 233818 233820 233822 233823 233824 233826 233827 233828 233830 233832 233836 233838 233842 233844 233848 233854 233856 233862 233866 233868 233872 233878 233884 233886 233892 233896 233898 233904 233908 233914 233922 266669
| A. | f(x)=$\sqrt{x}$ | B. | f(x)=lnx | C. | f(x)=($\frac{1}{2}$)x | D. | f(x)=tanx |