【简答题】知x>0,y>0,x+2y+xy=30,求xy的取值范围.
【单选题】— I hear Daming has gone to Hainan Island for his holiday. — Oh, how nice! Do you know when he ? [ ]
【简答题】己知:|x|=4,y 2 = 1 49 ;且x>0,y<0,求2x-7y的值.
【单选题】—I hear Sam has gone to Qingdao for his holiday. —Oh, how nice ! Do you know when he ? [ ]