g(x) =

f(x) = g(a  \cdot x + b) 

x

ax+b

g(x) = (1 / 3 * x^(3)) - x^(2)
a = 2.5 (slider from -5 to 5)
b = 1 (slider from -5 to 5)
f(x) = g((a * x) + b)
Eingabefeld1 = Textfield(g)
X = Point(xAxis)
Y: (a * X) + (b, 0)
sf = Segment(X, (x(X), f(x(X))))
sg = Segment(Y, (x(Y), g(x(Y))))