f(x) = (1 / 2 * x^(2)) - (2 * x) + 3
x0 = 3 (slider from -5 to 5, step 0.05)
A: (x0, f(x0))
h = 1.2 (slider from -3 to 3, step 0.01)
B: (x0 + h, f(x0 + h))
sekant = Line(A, B)
b: x = x0
c: x = x0 + h
d: y = f(x0)
e: y = f(x0 + h)
tangent = Tangent(A, f)