Sunday, 30 November 2014

sequences and series - What value does suminftyn=1dfrac14n2+16n+7 converge to?



What value does



n=114n2+16n+7


converge to?




Ok so I've tried changing the sum to:



n=116(2n+1)16(2n+7)



and then writting some values:
16·(13+15+17+12N+1)16·(19+111+113+12N+7)



but I don't know what else I can do to finish it! Any hint or solution?


Answer




Hint: Let's look at the 100th partial sum. It's good to get some concreteness.



16(13+15++1201)16(19++1205+1207).



We have a bunch of terms that are repeated: 19++1201 exists in each bracketed portion, so we can simply cancel all of them out to get



16(13+15+17120312051207).



Can you see how to use this line of reasoning to get the answer?


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