secante et deux tangentes
Author: Patrice Debart

f(x) = -(x) + sqrt(x^(2.0) + 4.0)
P = Point(xAxis)
a: x(P)
M: (a, f(a))
N: (-(a), f(-(a)))
t_M = Tangent(M, f)
t_N = Tangent(N, f)
dMN = Line(M, N)
PM = Segment(P, M)
I = Intersect(t_M, t_N)