19.已知函数f(x)=$\left\{\begin{array}{l}{3x-1,0≤x<1}\\{{2}^{x}-1,x≥1}\end{array}\right.$,设b>a≥0,若f(a)=f(b),则a•f(b)的取值范围是( )
| A. | [$\frac{2}{3}$,2) | B. | [-$\frac{1}{12}$,+∞) | C. | [-$\frac{1}{12}$,-$\frac{1}{3}$) | D. | [-$\frac{1}{3}$,$\frac{2}{3}$] |
18.若定义在R上的偶函数f(x)在[0,+∞)内是增函数,且f(3)=0,则关于x的不等式x•f(x)≤0的解集为( )
| A. | {x|-3≤x≤0或x≥3} | B. | {x|x≤-3或-3≤x≤0} | C. | {x|-3≤x≤3} | D. | {x|x≤-3或x≥3} |
17.已知函数y=f(x)定义在R上的奇函数,且当x≥0时,f(x)=x2-3x+b,则f(-2)=( )
0 234060 234068 234074 234078 234084 234086 234090 234096 234098 234104 234110 234114 234116 234120 234126 234128 234134 234138 234140 234144 234146 234150 234152 234154 234155 234156 234158 234159 234160 234162 234164 234168 234170 234174 234176 234180 234186 234188 234194 234198 234200 234204 234210 234216 234218 234224 234228 234230 234236 234240 234246 234254 266669
| A. | -2 | B. | 2 | C. | 10 | D. | -10 |