For x given, what do you think about the following limit?
lim
What I tried and what are the problems that I am facing:
Let f(x, n)=\left(x^n-1\right)^{1/n}. We have:
\log f(x, n)=\dfrac{1}{n}\log\left(x^n-1\right)=\dfrac{1}{n}\log\left(1-x^{-n}\right)+\dfrac{1}{n}\log\left(x^n\right),
first, I do not know if I can apply the log or not? I guess x must be real? and must be positive? what about complex?
Finally,
\lim_{n\to\infty}\left(x^n-1\right)^{1/n}=\log x.
Answer
Here is a down and dirty solution, for large n, (and assuming x>1, since otherwise how can you take n th root),
\frac{1}{2}x^n \leq x^n-1 \leq x^n
so
\frac{1}{\sqrt[n]{2}}x \leq (x^n-1)^{\frac{1}{n}} \leq x
So
(x^n-1)^{\frac{1}{n}} \to x
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