A = (r; Θ)

r

p = 0.5235988328204142 (slider from -6.283185307179586 to 6.28318531, step 0.26179939)
r(t) = 3 - (3 * cos(t - p))
a = CurveCartesian((r(t) * cos(t)), (r(t) * sin(t)), t, 0, 6.283185307179586)
A = Point(a)
u = Vector(A)
θ = Angle((2, 0), (0, 0), A)