a = 4 (slider from -5 to 10)
O: (0, 0)
c = Circle(O, a)
M = (7.48, 6.84)
f, g = Tangent(M, c)
A = Intersect(c, f, 1)
B = Intersect(c, g, 1)
C = Point(c)
t1, b, a_1, c_1 = Polygon(A, C, B)
α = Angle(A, M, B)
β = Angle(A, C, B)