3.若函数f(x)=ax-b的图象如图所示,则( )
A. | a>1,b>1 | B. | a>1,0<b<1 | C. | 0<a<1,b>1 | D. | 0<a<1,0<b<1 |
2.设椭圆C:$\frac{{x}^{2}}{{a}^{2}}+\frac{{y}^{2}}{{b}^{2}}=1(a>b>0)$的左焦点为(-2,0),离心率为$\frac{1}{2}$,则C的标准方程为( )
A. | $\frac{{x}^{2}}{16}+\frac{{y}^{2}}{12}=1$ | B. | $\frac{{x}^{2}}{16}+\frac{{y}^{2}}{4}=1$ | C. | $\frac{{x}^{2}}{12}+\frac{{y}^{2}}{8}=1$ | D. | $\frac{{x}^{2}}{16}+\frac{{y}^{2}}{8}=1$ |
14.在平行四边形ABCD中,AC=5,BD=4,则$\overrightarrow{AB}$•$\overrightarrow{BC}$=( )
0 252849 252857 252863 252867 252873 252875 252879 252885 252887 252893 252899 252903 252905 252909 252915 252917 252923 252927 252929 252933 252935 252939 252941 252943 252944 252945 252947 252948 252949 252951 252953 252957 252959 252963 252965 252969 252975 252977 252983 252987 252989 252993 252999 253005 253007 253013 253017 253019 253025 253029 253035 253043 266669
A. | $\frac{41}{4}$ | B. | -$\frac{41}{4}$ | C. | $\frac{9}{4}$ | D. | -$\frac{9}{4}$ |