d = 0.393 (slider from 0 to 1, step 0.001)
B = (15.24, -4.42)
A = (5.44, -4.3)
c = Semicircle(A, B)
a = Segment(A, B)
C = Point(c, d)
Vieleck1, b, a_1, c_1 = Polygon(A, C, B)
α = Angle(A, C, B)