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# OCR C2 HELP! Sigma Notation

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1. OCR C2 HELP! Sigma Notation
When i get questions with the sigma notation, I can't tell if the question is asking for the sum of an arithmetic or geometric progression. So i muddle up the formulae. Can someone tell me the difference if there is one.

Also for a question that says "Given that the geometric progression converges, find the exact value of r". How do I go about solving this? What does converge mean in terms of progressions. Thanks
Last edited by rokknroll3r; 17-05-2012 at 22:31.
2. Re: OCR C2 HELP! Sigma Notation
(Original post by rokknroll3r)
When i get questions with the sigma notation, I can't tell if the question is asking for the sum of an arithmetic or geometric progression. So i muddle up the formulae. Can someone tell me the difference if there is one.

Also for a question that says "Given that the geometric progression converges, find the exact value of r". How do I go about solving this? What does converge mean in terms of progressions. Thanks
I remember doing this paper, and from what I remember it's geometric.

Converges means it gets smaller and smaller. So the common difference will have to be between 0 and 1.
3. Re: OCR C2 HELP! Sigma Notation
Hi well the best thing to do is to calculate the first few terms, U1, U2, U3....this will give you 'a' and will show you whether there is a common difference 'd' or a common ratio 'r'. Therefore showing you whether it is a GP or an AP

Hope that made sense!

If something converges, it gets closer and closer to a particular value
Last edited by superhan; 17-05-2012 at 22:35.
4. Re: OCR C2 HELP! Sigma Notation
(Original post by rokknroll3r)
When i get questions with the sigma notation, I can't tell if the question is asking for the sum of an arithmetic or geometric progression. So i muddle up the formulae. Can someone tell me the difference if there is one.

Also for a question that says "Given that the geometric progression converges, find the exact value of r". How do I go about solving this? What does converge mean in terms of progressions. Thanks
work out each of the terms that its asking you to work out, probably the first 5 or 4, once you've done that then just add then up

Converges means that the series will never meet 0
5. Re: OCR C2 HELP! Sigma Notation
(Original post by djmoo)
Converges means that the series will never meet 0
I don't think that's true..
6. Re: OCR C2 HELP! Sigma Notation
Thanks for your help
7. Re: OCR C2 HELP! Sigma Notation
does anyone know where i can find a pdf of the Jan 2012 C2 paper?

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Last updated: May 17, 2012
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