t_A

y=x^2

Le rette tangenti t_A e t_B 
hanno uguale pendenza

k = 0 (slider from 0 to 3, step 0.1)
A = Point(c)
t_1 = Tangent(A, c)
B_1 = Point(t_1)
C = Point(t_1)
t = Segment(C, B_1)
d: y = x^(2) + k
B = Point(d)
a = Tangent(B, d)
E = Point(a)
D = Point(a)
t_B = Segment(D, E)
testo3: "" + d + ""
F = Point(d)
m = Slope(t_1)
m' = Slope(a)