R = 3.9 (slider from 0 to 10, step 0.1)
A = (5.8166, 6.6374)
B = (11.189, 2.4508)
a = Segment(A, B)
O = (12.3506, 4.9918000000000005)
c = Circle(O, R)
M = Point(c)
u = Vector(M, A)
v = Vector(M, B)
b = Line(A, v)
d = Line(B, u)
M' = Intersect(b, d)
w = Vector(M, M')