y=ax²

F(0;1/4a)

P(0; -1/4a)

O = Intersect(yAxis, xAxis)
a = 0.04 (slider from -5 to 2, step 0.01)
c: y = a * x * x
F: (0.0, 1.0 / (4.0 * a))
Δ: y = -1.0 / (4.0 * a)
M = Point(c)
b = Segment(M, F)
d = OrthogonalLine(M, Δ)
A = Intersect(Δ, d)
e = Segment(M, A)
B = Intersect(yAxis, Δ)