Exterior angles demonstration

Drag

k = 0.691 (slider from 0.0010 to 2, step 0.01)
C_1 = (12.36, -0.44)
D = (7.48, -5.36)
A = (5.036465116279057, 5.181860465116279)
B = (12.802976744186019, -0.4685581395348803)
α = 1.4835298641951802 rad (slider from 0 to 180*°, step 0.017453292519943295)
β = 0.8726646259971648 rad (slider from 0 to 180*°, step 0.017453292519943295)
a = Segment(A, B)
B' = Rotate(B, -α, A)
γ = Angle(B', A, B)
b = Line(A, B')
A' = Rotate(A, β, B)
δ = Angle(A, B, A')
c = Line(A', B)
C = Intersect(b, c)
poly1, b_1, a_1, e = Polygon(A, C, B)
E = PointIn(poly1)
d = Ray(E, A)
f = Ray(E, C)
g = Ray(E, B)
A'_1 = Dilate(A, k, E)
B'_1 = Dilate(B, k, E)
C' = Dilate(C, k, E)
poly2, c', a'_1, b'_1 = Polygon(A'_1, B'_1, C')
h = Ray(A'_1, C')
i = Ray(C', B'_1)
j = Ray(B'_1, A'_1)
ε = Angle(j, h)
ζ = Angle(h, i)
η = Angle(i, j)