# Evaluate $\lim_{n \to \infty}\left(\frac{1^{1/x}+2^{1/x}+\ldots+n^{1/x}}{n}\right)^{nx}$

$$\lim_{n \to \infty}\left(\frac{1^{1/x}+2^{1/x}+\ldots+n^{1/x}}{n}\right)^{nx}$$

I don't know any format or can't think of anything to solve this limit. It looks like it is Riemann's Sum Form but there is an x, so I am confused. Please help out. Thank You!

• Here can we treat x as constant?
– rash
Commented May 23, 2020 at 7:41
• Solution highly depends on $x$, say for $x=1$, limit is Infinite Commented May 23, 2020 at 7:47
• I think this limit is undefined or something. I have tried logging this expression to simplify. Ultimately, I get a Riemann's sum but multiplied with another limit which is certainly undefined.
– rash
Commented May 23, 2020 at 7:47
• I'm sure there's a typo somewhere (if not a mistake). Commented May 23, 2020 at 7:48
• Putting $x=1$ the expression becomes $((n+1)/2)^n$ which tends to $\infty$. Please fix typo in your question. Also remember that typos are more common in printed matter than most students think. Commented May 23, 2020 at 12:54

## 1 Answer

Lemma 1:

If the limit of $$(a_n)_{n\in\mathbb N}$$ exists or is infinite, then $$\lim_{n\to\infty}a_n=\lim_{n\to\infty}\frac1n\sum_{k=1}^na_k$$. Intuitively, the limit on the right is the average value of $$(a_n)_{n\in\mathbb N}$$, which is its limit. See here for more details.

Lemma 2:

If the limit of $$(a_n)_{n\in\mathbb N}$$ is $$\infty$$, then $$\lim_{n\to\infty}(a_n)^n=\infty$$.

Now it remains to see from lemma 1 that

$$\infty=\lim_{n\to\infty}n=\lim_{n\to\infty}\left(\frac1n\sum_{k=1}^nn^{1/x}\right)^x$$

and so the limit is $$\infty$$ for any $$x\ne0$$ by lemma 2.