Evaluate by a Riemann sum: $ \lim_{n \rightarrow \infty}\left(\frac {(n+1)^m+(n+2)^m+\cdots+(n+k)^m}{n^{m-1}}-kn\right)$
HINT:
$$\sum_{r=1}^k(n+r)^m=kn^m+\binom m1n^{m-1}\sum_{r=1}^kr+O(n^{m-2})$$
$$\frac {(n+1)^m+(n+2)^m+\cdots+(n+k)^m}{n^{m-1}}-kn$$ $$=\dfrac{\binom m1n^{m-1}\sum_{r=1}^kr+O(n^{m-2})}{n^{m-1}}$$ $$=\binom m1\sum_{r=1}^kr+O\left(\dfrac1n\right)$$