a = 0.1 (slider from -2 to 2, step 0.1)
f(x) = a * (x - 1.0) * (x - 5.0)
P = Point(f)
t = Tangent(P, f(x))
Text1: "f'(" + (x(P)) + ") = " + (f'(x(P)))
A: (x(P), f'(x(P)))
b = Segment(P, A)