题目内容
(Ⅰ)求向量c;
(Ⅱ)若映射f:(x,y)→(x′,y′),(x′,y′)=xa+2yc,若将P(x,y)看做动点的坐标,点(x′,y′)在圆C:x2+y2=8上运动,求点P(x,y)的轨迹方程;
(Ⅲ)若C、D是(Ⅱ)中轨迹上两个动点,M(0,2),求的范围.