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Mathematics 15 Online
OpenStudy (anonymous):

help!!

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

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

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..

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

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]

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

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