Wednesday, March 8, 2017

limits - Evaluate limlimitsntoinftyfrac1nlogleft(1+frac1nright)



lim



I start by writing \lim\limits_{n \to \infty} \frac 1n=0, and \lim\limits_{n \to \infty} \frac 1{n+\log \left ( 1\frac1n \right ) }=0



Since limit exists, by multiplication law, \lim\limits_{n \to \infty} \frac 1{n\log \left ( 1+\frac1n \right ) }=0




Hence the series \sum_{n}^{\infty }\frac{1}{n\log 1+\frac{1}{n}} converge.



However, the \lim n \to \infty \frac{1}{n\log \left ( 1+\frac{1}{n} \right ) } is given to be 1 in the solution, would really like to know where I've done wrong.



Thanks for the help.


Answer



Your first limit \lim_{n\to\infty}\frac{1}{n+\log(1+\frac{1}{n})}=0
In the corrected case we have \lim_{n\to \infty}\frac{1}{\log\left(1+\frac{1}{n}\right)^n}=1 since \lim_{n\to \infty}\log\left(1+\frac{1}{n}\right)^n=\log(e)=1 if \log means logarithmus naturalis, to the base e


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