x=ρ·cosθ;
y=ρ·sinθ;
则ρ^2=x^2 + y^2.
1
ρ=-10cosθ 则
ρ^2=-10cosθ ·ρ
∴x^2 + y^2 = -10x.
2
ρ=2cosθ-4sinθ 则
ρ^2=2cosθ ·ρ-4sinθ ·ρ
∴x^2 + y^2 =2x -4y