A = (-7, 6)
B = (-2, 3)
C = (1, 8)
D = (-3, 9)
veelhoek1, AB, b, CD, d = Polygon(A, B, C, D)
e = Line(A, B)
f = Line(D, C)
g = Segment(D, B)
h = OrthogonalLine(D, e)
i = OrthogonalLine(B, f)
E = Intersect(h, e)
F = Intersect(i, f)
DE = Segment(D, E)
BF = Segment(B, F)
α = Angle(B, E, D)
β = Angle(D, F, B)