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# C1 January 10th 2011 Exam (Edexcel) Watch

1. (Original post by chaosdestro0)
Very small chance you will need to know the proof of sum of series.
I am just trying to find it right now.
Edit:
Arithmetic proof

Sn = a + (a + d) + (a + 2d) + (a + 3d) + ..... (a + (n-2)d) + (a + (n-1)d)
Reversed Sn = (a + (n-1)d) + (a + (n-2)d) .... (a+ 3d) + (a+2d) + (a + d) + a

2Sn = 2a + (n - 1)d + 2a + (n-1)d + 2a(n-1)d

2sn = n[2a + (n-1)d]
Sn = n/2[2a + (n-1)d]
You clearly haven't looked at many papers if you think that. It has come up in the past and could easily come up again. I'm kinda hoping stuff like that does come up to catch some people out, although... I'm going for full marks so I don't really think people getting stuff right should affect me. Beginning to think C1 and C2 might be a bit of fun, I'll see if I still think that after I've completed the three hours.
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4. (Original post by Edwin Okli)
You clearly haven't looked at many papers if you think that. It has come up in the past and could easily come up again. I'm kinda hoping stuff like that does come up to catch some people out, although... I'm going for full marks so I don't really think people getting stuff right should affect me. Beginning to think C1 and C2 might be a bit of fun, I'll see if I still think that after I've completed the three hours.
I have done many past papers and have yet to see this, can you give me an example of this question.
have checked : 2009 c1 June and january nope
2010 june- Nope
2006 January- Nope
2007 June-Nope

I have done a fairly large amount of papers and have not seen a questions asking for proof as far as I can remember
Just remember that I started revision in november so it is fairly long ago.
5. (Original post by chaosdestro0)
I have done many past papers and have yet to see this, can you give me an example of this question.
June 2005
Q9a) Prove that the sum of the first n terms of the series is 1/2 n[2a + (n ?1)d].
First example I found, not sure if it did come up again after that. But that doesn't mean it isn't likely to come up tomorrow.
6. Good luck for the exam tomorrow people. Hope all goes well.
7. Good luck everyone!!
8. @people who helped with formula's

Thanks Guys

____________

Like most of you I am really worried about making silly mistakes.

I make the most stupid mistakes and lost 15 marks in the specimen because of that, but then in some papers I make hardly any silly mistakes!
9. Good luck everyoneeee!
10. BTW does anyone have links to how your prove those arithmetic/geometric series formula's?!!!
11. (Original post by Darthdevidem)
BTW does anyone have links to how your prove those arithmetic/geometric series formula's?!!!
If you've got an arithmetic series with n terms

Call the sum of these terms

So

If you rewrite the same sum, but in reverse, you get

If you do you can see the terms are identical.

By this I mean, you end up with:

The terms are symmetrical, you're increasing the common difference with and you're decreasing the common difference with . Because there are n terms, you end up with n many

So

For a geometric series, if you've got the series with n terms

Then the sum of these n terms,

If you multiply by

You can see that all the terms of are identical to those of bar the in and the in

So if you subtract the second equation from you end up with

I might as well go on to explain how you obtain the sum to infinity formula from this, for when

If you got the formula

and you're summing it to infinity:

Providing , , you can try this on your calculator, the value of r will tend to zero as you keep on multiplying it by r.

So, because , and so

12. {mod: exam discussion removed}
13. Mod: exam discussion removed
14. You cannot discuss this exam until midnight. Please read the related announcement.
15. Mod: exam discussion removed.
16. My bad, I thought we could discuss the hardness of it lol x
17. The announcement is very clear:

This means no discussion AT ALL - not even "I found it hard/easy" or "I dropped my pencil". The line between

* "I found it hard" and
* "I found question 2 hard" and
* "I found question 2 about <insert subject> hard"
18. You cannot discuss this exam until midnight.
19. mod: text removed
20. cant discuss it .

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