Mathematics
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OpenStudy (anonymous):
help!!
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OpenStudy (anonymous):
OpenStudy (kc_kennylau):
For a series to be convergent, \(\Large\displaystyle\lim_{n\rightarrow\infty}\left|\frac{a_{n+1}}{a_n}\right|<1\)
OpenStudy (kc_kennylau):
That means \(\Large\displaystyle\lim_{n\rightarrow\infty}\left|\frac{\frac1{(n+1)(\ln (n+1))^p}}{\frac1{n(\ln n)^p}}\right|<1\)
OpenStudy (anonymous):
how do u find p from ratio test? i got n/(n+1)(ln n)^p
OpenStudy (kc_kennylau):
Where did the ln(n+1) go? :O
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OpenStudy (anonymous):
i thought that would be canclled out by ln n haha
OpenStudy (anonymous):
okay i might be wrong for that. pls, show me how T^T
OpenStudy (kc_kennylau):
Well you'd get n/(n+1)[ln(n)/ln(n+1)]^p
OpenStudy (anonymous):
okay, then after that? there are 2 variables, n and p
OpenStudy (kc_kennylau):
n is set to infinity
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OpenStudy (kc_kennylau):
I think l'hopital should be used here?
OpenStudy (anonymous):
that would be a lttle complicated
OpenStudy (kc_kennylau):
Well...
OpenStudy (kc_kennylau):
You do notice n/(n+1) = 1
OpenStudy (anonymous):
yes..
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OpenStudy (kc_kennylau):
You do notice (ln n)^p is differentiable
OpenStudy (anonymous):
u mean (lnn/ln(n+1))^p
OpenStudy (kc_kennylau):
No coz l'hopital
OpenStudy (anonymous):
i'm confused, can you break it down clearly/
OpenStudy (kc_kennylau):
Well I'm sick so my brain ain't propering functionly
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OpenStudy (anonymous):
\[\lim_{n \rightarrow \infty} \frac{ n }{ (n+1)[\frac{ \ln n }{ \ln (n+1) }]^p }\]
OpenStudy (anonymous):
hmm okay then,
OpenStudy (kc_kennylau):
n/(n+1)[(ln n)^p/(ln n+1)^p]
OpenStudy (kc_kennylau):
i.e. [(ln n)^p/(ln n+1)^p]
OpenStudy (kc_kennylau):
l'hopital: [p(ln n)^(p-1)/n]/[p(ln n+1)^(p-1)/n]
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OpenStudy (anonymous):
so it will be pln^(p-1)/pln(n+1)^p-1
OpenStudy (anonymous):
all that <1 ?
OpenStudy (kc_kennylau):
Well
OpenStudy (kc_kennylau):
I actualy don't know... I'm so dizzy now
OpenStudy (anonymous):
i'm sorry u shd go rest