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FP1 Edexcel Question (Series)

How would I go about a question if it's 'n' in the series and not 'r'? I'm doing question 10 (ii) but I don't understand the mark scheme.

http://pmt.physicsandmathstutor.com/download/Maths/A-level/FP1/Papers-Edexcel-Tiered/06%20Gold%202%20-%20FP1%20Edexcel.pdf
Original post by amelienine
How would I go about a question if it's 'n' in the series and not 'r'? I'm doing question 10 (ii) but I don't understand the mark scheme.

http://pmt.physicsandmathstutor.com/download/Maths/A-level/FP1/Papers-Edexcel-Tiered/06%20Gold%202%20-%20FP1%20Edexcel.pdf


∑r=0n2n\sum\limits_{r=0}^n 2n means for each value of rr, the corresponding term is 2n2n, which is independent of rr. There are n+1n+1 values of rr.

Hence ∑r=0n2n=2n(n+1)\sum\limits_{r=0}^n 2n = 2n(n+1).
(edited 7 years ago)
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Avatar for amelienine
amelienine
OP
12
Original post by SherlockHolmes
∑r=0n2n\sum\limits_{r=0}^n 2n means for each value of rr, the corresponding term is 2n2n, which is independent of rr. There are n+1n+1 values of rr.

Hence ∑r=0n2n=2n(n+1)\sum\limits_{r=0}^n 2n = 2n(n+1).


Why are there n+1 vales of r?
Original post by amelienine
Why are there n+1 vales of r?


r=0,1,...,nr = 0,1,...,n.

I think of this as nn values from 11 to nn and then you add 11 for 0.
Reply 4
Avatar for amelienine
amelienine
OP
12
Original post by SherlockHolmes
r=0,1,...,nr = 0,1,...,n.

I think of this as nn values from 11 to nn and then you add 11 for 0.


Oh okay, thank you!

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