Solution (source code)

= Solution

For an $N+1$ times continuously differentiable <function>, <Taylor's theorem> gives
$$
\boxed{f(x)=\sum_{n=0}^N\frac{f^{(n)}(x_0)}{n!}(x-x_0)^n+\frac{f^{(N+1)}(\xi)}{(N+1)!}(x-x_0)^{N+1},}
$$
where $\xi$ lies between $x_0$ and $x$. An infinite <Taylor series> represents the function when its remainder tends to zero; this holds locally for an <analytic function>, rather than for every smooth function automatically.