f(x) =

k(x) = 1 - sqrt(1 - x^(2))
f(x) = (0.5 * x^(4)) + (0.5 * x^(2))
Eingabefeld1 = Textfield(f)
f1(x) = f'(x)
Text1: "f'(x) = " + (LaTeX[f1]) + ""