f(x) = f(x_0) + f'(x_0)(x - x_0) + \frac{f^{(2)}(x_0)}{2!}(x-x_0)^2 + ...+  \frac{f^{(n)}(x_0)}{n!}(x-x_0)^n  + o((x-x_0)^n)