g(x) =

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

x

ax

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