Tuesday, December 5, 2017

calculus - How to find the limit limlimitsntoinfty1/sqrt[n]n which is indeterminate on evaluation but is convergent?



When I evaluate the limit in the title above I get the following:



lim




But when I use a computer software (mathematica) to evaluate the same limit it says the limit is 1. What am I doing wrong?


Answer



Indeterminate forms can have values.



Note from L'Hospital's Rule that \lim_{n\to \infty}\frac{\log(n)}{n}=\lim_{n\to \infty}\frac{1/n}{1}=0. Hence, we have



\begin{align} \lim_{n\to \infty}\frac{1}{n^{1/n}}&=\lim_{n\to \infty}e^{-\frac1n \log(n)}\\\\ &e^{-\lim_{n\to \infty}\left(\frac1n \log(n)\right)}\\\\ &=e^0\\\\ &=1 \end{align}



as expected!


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