avviare l'animazione

t = 3.3 (slider from -10 to 10, step 0.1)
f = 1 (slider from -5 to 5, step 0.1)
F: (0, f)
a: y = (-f)
b = OrthogonalLine(F, a)
G = Intersect(a, b)
d: x^(2) + (y - f)^(2) = (t + f)^(2)
c: y = t
C, D = Intersect(d, c)
e: y = (1 / ((4 * f)) * x^(2))
H: (0, t)