F = Point(yAxis)
b = 2.7 (slider from -5 to 5, step 0.1)
D: y = b
A = Point(D)
Δ_A = LineBisector(F, A)
δ_A = OrthogonalLine(A, D)
M = Intersect(Δ_A, δ_A)
loc1 = Locus(M, A)