Friday, 26 September 2014

calculus - is $sumlimits _{n=1}^{infty}lnleft(frac{left(n+1right)^{2}}{nleft(n+2right)}right)



I don't know why but I'm having a hard time determining whether this series
n=1ln((n+1)2n(n+2))
converges to a real limit.




I did try to break it down according to ln identities.
ln((n+1)2n(n+2))=ln((n+1)2)ln(n(n+2))=2ln(n+1)lnnln(n+2)
and then tried to increase it to get to a series that converges to a real number:
2ln(n+1)lnnln(n+2)2ln(n+1)lnnln(n+1)=ln(n+1)lnn
so Sn will be like that
Sn=ln2ln1+ln3ln2++ln(n+1)lnn=ln(n+1)ln1=ln(n+1)
and so lim



I know this series does converge to a real number (Well according to Wolfram Alpha :) \ )



Any help would be appreciated.


Answer



Hint:





Theorem: Let \lim_{n\to\infty}n^pu_n=A. \sum u_n converges if p>1 and A is finite.




Now take p=2.


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