TITLE: How to prove $\lim_{n \to \infty} \sqrt{n}(\sqrt[n]{n} - 1) = 0$?
QUESTION [13 upvotes]: I want to show that $$\lim_{n \to \infty} \sqrt{n}(\sqrt[n]{n}-1) = 0$$ and my assistant teacher gave me the hint to find a proper estimate for $\sqrt[n]{n}-1$ in order to do this. I know how one shows that $\lim_{n \to \infty} \sqrt[n]{n} = 1$, to do this we can write $\sqrt[n]{n} = 1+x_n$, raise both sides to the n-th power and then use the binomial theorem (or to be more specific: the term to the second power). However, I don't see how this or any other trivial term (i.e. the first or the n-th) could be used here. 
What estimate am I supposed to find or is there even a simpler way to show this limit?
Thanks for any answers in advance.

REPLY [11 votes]: An elementary proof using $\text{AM} \ge \text{GM}$:
We have that, for sufficiently large $n$, 
$$ \frac{1 + 1 + \dots + 1 + n^{1/3} + n^{1/3} + n^{1/3}}{n} \ge n^{1/n}$$
using $\text{AM} \ge \text{GM}$ on $n-3$ copies of $1$ and three copies of $n^{1/3}$.
i.e we get the estimate
$$ 1 - \frac{3}{n} + \frac{3}{n^{2/3}} \ge n^{1/n}$$
This proof can be generalized to show that
$$n^{(k-1)/k} (n^{1/n} - 1) \to 0$$
for any positive integer $k$.
A variant of: Proof that $\lim_{n\rightarrow \infty} \sqrt[n]{n}=1$