方程化为(x-2)²+y²=5.令x=2+√5cosθ,y=√5sinθ,y-x=√5sinθ-(2+√5cosθ)=√10sin(θ-π/4)-2,最大√10-2,最小-√10-2.x²+y²=(2+√5cosθ)²+(√5sinθ)²=9+4√5cosθ,最大9+4√5,...