A = (-3, 0)
B = (6, 5)
a = Line(A, B)
C = (7, 0)
b = Line(A, C)
D = Point(a)
c = OrthogonalLine(D, a)
d = OrthogonalLine(D, b)
E = Intersect(b, d)
F = Intersect(b, c)
u = Vector(E, F)
e = 0.32 (slider from 0 to 1, step 0.01)
M: E + e * u
poly1, m, a_1, d_1 = Polygon(A, D, M)