ρ=4sinθ
ρ^2=4ρsinθ
x^2+y^2=4y
x^2+(y-2)^2=4
圆心为(0,2).
点A(4,π/6)
(2根号3,2).
点A(4,π/6)到圆心C的距离=根号(12)=2根号3.