Teorema do Ângulo Externo
Author: OBMEP_ SRG

A = (-2, -1)
B = (7.32, 5.1)
C = (10, -1)
pol1, c, a, b = Polygon(A, B, C)
D = (14.34, -1)
d = Segment(C, D)
α = Angle(C, A, B)
β = Angle(A, B, C)
λ = Angle(D, C, B)
s = Sum({α, β})
γ = Angle(B, C, A)