Foci of Ellipse Construction
Author: M. Dabbs, R. Walcott

Move the points A and B

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(a, b)

A_1 = Point(a)
b = OrthogonalLine(A_1, a)
A = Point(a)
c = Circle(A_1, A)
B = Point(b)
d = Circle(A_1, B)
D = Point(d)
e = Line(A_1, D)
f = Line(D, a)
E = Intersect(c, e, 2.0)
g = Line(E, b)
F = Intersect(g, f)
loc1 = Locus(F, D)
h = Circle(B, Segment[A_1, A])
S_1, S_2 = Intersect(h, a)
k = Circle(A, Segment[A_1, B])
F_1, F_2 = Intersect(k, b)