r = 1.5 (slider from 0.2 to 5, step 0.1)
O = (-1.7, 4.1)
c = Circle(O, r)
B = Point(c)
A = Point(c)
a = Segment(B, A)
b = Tangent(A, c)
C = Point(b)
d = Segment(A, C)
α = Angle(B, A, C)
e = OrthogonalLine(O, a)
M = Intersect(c, e, 1)
f = Segment(O, A)
g = Segment(O, M)
β = Angle(M, O, A)
h = CircleArc(O, B, A)