Author: Fabrice Eudes (d'après manuel Sésamath 4e, p139)

R = 1 (slider from 0 to 5, step 0.1)
α = 0 (slider from -440 to 440, step 1)
x_C: R α 2 * 3.14 / 360
C: (x_C, R)
c = Circle(C, R)
H = Intersect(c, xAxis, 1)
A = Rotate(H, -3.14159 α / 180, C)
a = Segment(C, A)
b = Segment(C, H)