def f(x):
    return ((-41*x**4)/12) + ((79*x**3)/6) - ((49*x**2)/12) - ((44*x)/3) + 5
def fderiv(x, deltax):
    return (f(x + deltax) - f(x - deltax)) / 2 * deltax
print fderiv(f(0), 0.25)
-48.736328125
print fderiv(f(0), 0.1)
-7.76885