k = 0.7 (slider from 0 to 5, step 0.1)
f_k(x) = exp((k * x))
g_k(x) = exp(((-k) * x))
M = Point(f_k)
N: (x(M), g_k(x(M)))
T = Tangent(M, f_k)
D = Tangent(N, g_k)
A = Intersect(T, xAxis)
B = Intersect(D, xAxis)
b = Segment(A, B)
I = Midpoint(b)