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# FP1 hard question Watch

1. Hello, I know this question has been answered several times but I just cannot seem to understand the mark scheme or any of the explanations? It is the second part of course - I have no idea how the 2n is manipulated or how it is turned into what it is turned into. If someone could try and explain it I'd be grateful!! Thank you
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2. (Original post by iMacJack)
Hello, I know this question has been answered several times but I just cannot seem to understand the mark scheme or any of the explanations? It is the second part of course - I have no idea how the 2n is manipulated or how it is turned into what it is turned into. If someone could try and explain it I'd be grateful!! Thank you
The is just a constant. So
3. (Original post by Zacken)
The is just a constant. So
Am I right in assuming if the series was from r = 1 to n instead of r = 0 to n it would be (2n+1)(n) instead of (2n+1)(n+1) basically, is it (n+1) because the extra term is involved due to it beginning from 0 instead of one? Thank you
4. (Original post by iMacJack)
Am I right in assuming if the series was from r = 1 to n instead of r = 0 to n it would be (2n+1)(n) instead of (2n+1)(n+1) basically, is it (n+1) because the extra term is involved due to it beginning from 0 instead of one? Thank you
Yep! Bang on.

I've answered this very question at least four times this past month, seems like it trips up a lot of people.
5. (Original post by Zacken)
Yep! Bang on.

I've answered this very question at least four times this past month, seems like it trips up a lot of people.
Haha yes it does indeed!! What if I just dealt with the 2n separately to the + 1 instead of combining it to 2n+1(n+1)?
6. (Original post by iMacJack)
Haha yes it does indeed!! What if I just dealt with the 2n separately to the + 1 instead of combining it to 2n+1(n+1)?
Well, you'd get the same thing:

7. (Original post by Zacken)
Well, you'd get the same thing:

Of course!
Many thanks
8. (Original post by iMacJack)
Of course!
Many thanks
No worries, good luck for the exam!
9. (Original post by Zacken)
No worries, good luck for the exam!
Thank you, I'll definitely be needing that luck... haha

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