Demonstração:

∡EAD=∡ACD+∡CDA=2∡ACD
∡BAE=∡ACB+∡ABC=2∡BCA
logo,
β=2α

A = (5.4, 0.6)
B = (2.98, -3.58)
c = Circle(A, B)
C = Point(c)
D = Point(c)
a = Segment(C, B)
b = Segment(B, A)
d = Segment(A, D)
e = Segment(D, C)
α = Angle(B, C, D)
β = Angle(B, A, D)
f = Line(C, A)
E = Intersect(c, f, 2)