已知是椭圆的两个焦点,过的直线交椭圆于两点,若的周长为,则椭圆方程为( )
已知全集,,,,则()
在①.1{0,1,2,3};②.{1}∈{0,1,2,3};③.{0,1,2,3}{0,1,2,3}; ④.{0}上述四个关系中,错误的个数是:()
设集合的真子集个数是()