Friday, 10 May 2019

limits - $limlimits_{n rightarrow +infty} frac{sumlimits_{k=1}^{n} sqrt[k] {k} }{n}= 1$



I would like to prove that:




$$\lim\limits_{n \rightarrow +\infty} \frac{\sum\limits_{k=1}^{n} \sqrt[k] {k} }{n}= 1$$



I thought to write $\sqrt[k] {k} = e^{\frac{\ln({k})}{k}}$ but I don't know how to continue.


Answer



Use Stolz–Cesàro theorem or a version of it here.



$$\lim\limits_{n \rightarrow +\infty} \frac{\sum\limits_{k=1}^{n+1} \sqrt[k] {k} -\sum\limits_{k=1}^{n} \sqrt[k] {k} }{n+1 - n}=
\lim\limits_{n \rightarrow +\infty}\sqrt[n+1] {n+1} =1$$


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