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# C2 - Geometric Sequences (resolved) watch

1. I can't rearrange, it seems. Anywho, fixed.
OCR C1/C2 book, p342 Ex 6B
Find the sum of the following geometric series:
So I tried it, using ari-1 to find the ith term and ended up with and i-1=n therefore i=n+1. I then put it into the formula: and rearranged to get ...which is wrong. The book gives , implying that the ith term is n.

I had the same problem with the next two questions - where am I going wrong? Why is the ith term n and not n+1 with these? Thanks.
OCR C1/C2 book, p342 Ex 6B

So I tried it, using ari-1 to find the ith term and ended up with and i-1=n therefore i=n+1. I then put it into the formula: and rearranged to get ...which is wrong. The book gives , implying that the ith term is n.

I had the same problem with the next two questions - where am I going wrong? Why is the ith term n and not n+1 with these? Thanks.
I won't comment on what you're saying about the ith term, as I'm not clear what you mean.

However, your initial formula is correct; you're going wrong when you re-arrange it.

3. (Original post by ghostwalker)
I won't comment on what you're saying about the ith term, as I'm not clear what you mean.

However, your initial formula is correct; you're going wrong when you re-arrange it.

*facepalm* Thanks, I now feel like a pillock

As soon as I saw the halfn+1 over a half, it clicked. I think I was just laying it out awkwardly so that I couldn't see where I was going. Oopsie.

Merci buckets.

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Updated: April 3, 2011
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