c = -1.5 (slider from -5 to 5, step 0.1)
f(x) = 3 * x / (x^(2) + 1)
A = Intersect(f, xAxis, (0, 0))
a = Tangent(A, f)
b = 3 (slider from -5 to 5, step 0.1)
B: (b, f(b))
c_1 = Tangent(B, f)
C: (c, f(c))
e = Tangent(C, f)