A = Intersect(xAxis, yAxis)
B = (1, 0)
c = Circle(A, B)
β = 0 rad (slider from 0 to 90°, step 5°)
B' = Rotate(B, β, A)
f = Line(B, yAxis)
g = Ray(A, B')
C = Intersect(f, g)
α = Angle(xAxis, g)