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)−lnn−ln(n+2)
and then tried to increase it to get to a series that converges to a real number:
2ln(n+1)−lnn−ln(n+2)≤2ln(n+1)−lnn−ln(n+1)=ln(n+1)−lnn
so Sn will be like that
Sn=ln2−ln1+ln3−ln2+⋯+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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