  $ f_a(x)\,=\,x^2\hspace{0.2ex} e^{1- \frac{x}{a}} $

a = 1.4 (slider from -5 to 5, step 0.1)
f(x) = x^(2) * exp(1 - x / a)
f'(x) = f'(x)
g(x) = x^(2) / exp(1)