17.已知等比数列{an}中,a2=2,又a2,a3+1,a4成等差数列,数列{bn}的前n项和为Sn,且$\frac{1}{{S}_{n}}$=$\frac{1}{n}$-$\frac{1}{n+1}$,则a8+b8=( )
| A. | 311 | B. | 272 | C. | 144 | D. | 80 |
16.已知sin(α+$\frac{π}{6}$)+cosα=$\frac{4}{5}$$\sqrt{3}$,则cos(2α+$\frac{2π}{3}$)的值为( )
| A. | -$\frac{7}{25}$ | B. | $\frac{7}{25}$ | C. | $\frac{9}{25}$ | D. | -$\frac{9}{25}$ |
15.在倾斜角等于30°的山坡上竖立一根旗杆,当太阳在山顶上方时,从山脚看太阳的仰角是60°,旗杆此时在山坡上的影子长是25米,则旗杆高为( )
| A. | 25米 | B. | 12.5米 | C. | 22米 | D. | 30米 |
14.已知sinα+cosα=$\sqrt{2}$,α∈(0,π),则tanα=( )
0 227706 227714 227720 227724 227730 227732 227736 227742 227744 227750 227756 227760 227762 227766 227772 227774 227780 227784 227786 227790 227792 227796 227798 227800 227801 227802 227804 227805 227806 227808 227810 227814 227816 227820 227822 227826 227832 227834 227840 227844 227846 227850 227856 227862 227864 227870 227874 227876 227882 227886 227892 227900 266669
| A. | -1 | B. | -$\frac{\sqrt{2}}{2}$ | C. | $\frac{\sqrt{2}}{2}$ | D. | 1 |