简化的北京奥运会主体育场“鸟巢”的钢结构俯视图如图所示,内外两圈的钢骨架是离心率相同的椭圆,外层椭圆顶点向内层椭圆引切线AC,BD,设内层椭圆方程为 x 2 a 2 + y 2 b 2 =1(a>b>0) ,则外层椭圆方程可设为 x 2 (ma) 2 + y 2 (mb) 2 =1(a>b>0,m>1) .若AC与BD的斜率之积为 - 9 16 ,则椭圆的离心率为( )
【单选题】A 38-year-old male patient with a gastric ulcer is treated successfully with the drug omeprazole. The basis for omeprazole inhibition of gastric H + secretion is that it
【简答题】Katherine Com male is an 11-year-old girl from Pennsylvania. At the age of five she began raising money to buy nets for children in Africa to help stop the spread of malaria(疟疾). When she was five, Ka...