16.已知下列三个方程:x2+2ax+2a+3=0,x2+2(a+1)x+a2=0,x2+2ax-2a=0至少有一个方程有实数根,则实数a的取值范围为( )
| A. | (-∞,-1]∪[2,+∞) | B. | (-1,2) | C. | (-∞,-1]∪[-$\frac{1}{2}$,+∞) | D. | (-1,-$\frac{1}{2}$) |
15.已知函数f(x)=$\frac{x}{x-2}$,则f′(1)=( )
| A. | 1 | B. | 2 | C. | -1 | D. | -2 |
9.若sin4x<cos4x,则x的取值范围是( )
0 229679 229687 229693 229697 229703 229705 229709 229715 229717 229723 229729 229733 229735 229739 229745 229747 229753 229757 229759 229763 229765 229769 229771 229773 229774 229775 229777 229778 229779 229781 229783 229787 229789 229793 229795 229799 229805 229807 229813 229817 229819 229823 229829 229835 229837 229843 229847 229849 229855 229859 229865 229873 266669
| A. | $\left\{{\left.x\right|2kπ-\frac{3}{4}π<x<2kπ+\frac{π}{4},k∈Z}\right\}$ | B. | $\left\{{\left.x\right|2kπ+\frac{π}{4}<x<2kπ+\frac{5}{4}π,k∈Z}\right\}$ | ||
| C. | $\left\{{\left.x\right|kπ-\frac{π}{4}<x<kπ+\frac{π}{4},k∈Z}\right\}$ | D. | $\left\{{\left.x\right|kπ+\frac{π}{4}<x<kπ+\frac{3}{4}π,k∈Z}\right\}$ |