'General method for the taylor term.
This method is slow, because it differentiates n-times. Subclasses can
redefine it to make it faster by using the "previous_terms".'

def taylor_term(self, n, x, *previous_terms):

    from sympy import Dummy, factorial
    x = sympify(x)
    _x = Dummy('x')
    return ((self.subs(x, _x).diff(_x, n).subs(_x, x).subs(x, 0) * (x ** n)) / factorial(n))
