Solution
= Solution
The ordinary mean value theorem gives $\Delta_hf(a)=hf'(b_1)$ for some $b_1\in(a,a+h)$. More generally, applying it to the difference of two translated <functions> shows inductively that
$$
\Delta_h^kf(a)=h^kf^{(k)}(b_k)
$$
for some $b_k\in(a,a+kh)$. Taking $k=n$ proves the result.