15.已知不等式组$\left\{\begin{array}{l}{x+y-4≤0}\\{x-4y+1≤0}\end{array}\right.$所表示的平面区域为M,不等式组$\left\{\begin{array}{l}{2x-3y-3≥0}\\{2x+2y-3≤0}\end{array}\right.$所表示的平面区域为N,若M中存在点在圆C:(x-3)2+(y-1)2=r2(r>0)内,但N中不存在点在圆C内.则r的取值范围是( )
| A. | (0,$\frac{\sqrt{13}}{2}$] | B. | ($\frac{\sqrt{13}}{2}$,$\sqrt{17}$) | C. | (0,$\sqrt{17}$) | D. | (0,$\frac{5\sqrt{2}}{4}$) |
13.cos$\frac{π}{7}$cos$\frac{3π}{7}$cos$\frac{5π}{7}$的值为( )
| A. | $\frac{1}{4}$ | B. | -$\frac{1}{4}$ | C. | $\frac{1}{8}$ | D. | -$\frac{1}{8}$ |
10.设数列{an}和{bn}分别是等差数列与等比数列,且a1=b1=9,a7=b7=1,则以下结论正确的是( )
0 227796 227804 227810 227814 227820 227822 227826 227832 227834 227840 227846 227850 227852 227856 227862 227864 227870 227874 227876 227880 227882 227886 227888 227890 227891 227892 227894 227895 227896 227898 227900 227904 227906 227910 227912 227916 227922 227924 227930 227934 227936 227940 227946 227952 227954 227960 227964 227966 227972 227976 227982 227990 266669
| A. | a3<a4 | B. | a4>b4 | C. | a4<b4 | D. | b3<b4 |