求动点（2-cosθ,cos2θ）的轨迹的普通方程x=2-cosθ,故cosθ=2-x；于是cos²θ=(2-x)².(1)y=cos2θ=1-2sin²θ；故sin²θ=(1-y)/2.(2)(1)+(2)得(2-x)²+(1-y)/2=1即y=2(x-2)²-1=2x&su...