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+17−1203−1205−1207).
Can you see how to use this line of reasoning to get the answer?
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