实数x,y满足（x-1）^2+(y+2)^2=5设为参数方程为 x=1+√5cosθ y=-2+√5sinθ x-2y =1+√5cosθ-2(-2+√5sinθ) =5-(2√5sinθ-√5cosθ) =5-√(2√5^2+√5^2)=5-5sin(θ+φ）要值最大,则sin(θ+φ）最小为-1(x-2y)ma...