A_{1} = (9.56, -4.62)
B = (19.72, -6.26)
f = Line(A_{1}, B)
S_1 = Point(f)
D = Point(f)
k_1 = Circle(S_1, D)
S_2 = Point(f)
k_2 = Circle(S_2, D)
A = Intersect(k_2, f, 2)
a = 0 (slider from 0 to 3, step 1)
C = Intersect(k_1, f, 2)
S_3 = Midpoint(C, A)
k_3 = Circle(S_3, A)