Friday, 9 October 2015

sequences and series - Show that sumlimitsin=1nftyfrac2n213n5+2n+1 converges or diverges

I'm working with some infinite series problems and I have to show that the series
n=12n213n5+2n+1 converges or diverges. I don't have a lot of experience doing this yet, and this is a problem that my teacher made up so I have no way to check my answer.



For this problem, I said the series converges by direct comparison with 23n=11n3 which converges by the p-series test. However, I'm not sure if I did this correctly and if all of the steps I took were "legal". This is my reasoning:



2n213n5+2n+12n23n5 for all n.




bn=2n23n5=23n3



n=123n3=23n=11n3 which converges by the p-series test.



Therefore, n=12n213n5+2n+1 converges by the direct comparison test with n=11n3.



Could anyone verify I used the test correctly or point out my mistakes? Thank you.

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