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Mathematics 15 Online
OpenStudy (anonymous):

Help..

OpenStudy (anonymous):

How can i apply integral test to this \[\frac{ 1 }{ k( Logk)^{p}}\]

OpenStudy (anonymous):

what are the limits ? 2 to infinity ?

OpenStudy (anonymous):

yes..

OpenStudy (anonymous):

\(\large \sum \limits_2^{\infty } \frac{1}{k (\ln k)^p} \) converges \(\iff\) \(\large \int \limits_2^{\infty} \frac{1}{k(\ln k )^p}dk \) is finite

OpenStudy (anonymous):

\(\large \sum \limits_2^{\infty } \frac{1}{k (\ln k)^p} \) diverges \(\iff\) \(\large \int \limits_2^{\infty} \frac{1}{k(\ln k )^p}dk \) is not finite

OpenStudy (anonymous):

For which p the integral is finite ?

OpenStudy (anonymous):

evaluate the right side integral and see when it is finite

OpenStudy (anonymous):

p is greater than 1 ?

OpenStudy (anonymous):

ln k = u 1/k dk = du \(\large \int \limits_{\#}^{*} 1/t^p dt\) analyze this

OpenStudy (anonymous):

\(\large \frac{t^{-p+1}}{-p+1} \Big|_{\ln 2}^{\infty } \)

OpenStudy (anonymous):

when p < 1, clearly it diverges

OpenStudy (anonymous):

p =1 also it diverges p > 1 is when it wud be finite,

OpenStudy (anonymous):

let me know if u want discuss the reasoning behind these 3 conclusions

OpenStudy (anonymous):

why at p=1 diverges? because its result becomes 0/0 then the integral is undefined ?

OpenStudy (anonymous):

nope

OpenStudy (anonymous):

\(\large \int \limits_{\ln 2}^{\infty} 1/t dt = \ln t \Big|_{\ln 2}^{\infty} = \ln \infty - **** = \infty \)

OpenStudy (anonymous):

so, p = 1 also diverges

OpenStudy (anonymous):

thank you..

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