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# FP1 Summation Series when r=0 watch

1. I don't know what to do when you get a summation series where r=0

To be more specific, question 10ii, paper June 2013 (R) from Edexcel:
https://gyazo.com/501ce98024b3cbff43cdc682dc6bb5a2
(above is the screenshot of the question)

I've read through the mark scheme but I genuinely don't understand
https://gyazo.com/2425b703b74bbd62fe5cb2fb2e8d3c45

Could anyone please explain what you have to do when r=0, and what do you do when you are given a series with 'n' in (that is 'n' mixed up with 'r'). I know how to expand with 'r's, but with 'n'... I don't know

Thank you!
2. (Original post by Horagontus)
I don't know what to do when you get a summation series where r=0

To be more specific, question 10ii, paper June 2013 (R) from Edexcel:
https://gyazo.com/501ce98024b3cbff43cdc682dc6bb5a2
(above is the screenshot of the question)

I've read through the mark scheme but I genuinely don't understand
https://gyazo.com/2425b703b74bbd62fe5cb2fb2e8d3c45

Could anyone please explain what you have to do when r=0, and what do you do when you are given a series with 'n' in (that is 'n' mixed up with 'r'. I know how to expand with 'r's, but with 'n'... I don't know

Thank you!
First split it up into three seperate sums:

Note that the first two sums have the leading term = 0 because 0^2=0 and 0=0. The last term is simply the sum of (n+1) terms all of which each the constant value (2n+1).
3. (Original post by Horagontus)

Could anyone please explain what you have to do when r=0, and what do you do when you are given a series with 'n' in (that is 'n' mixed up with 'r'. I know how to expand with 'r's, but with 'n'... I don't know

Thank you!
Two ways to look at it:

1.

2. .

Since in this case you have

Then you have being added together times to get a total of .

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