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FP1 Series Question... Need help please..

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    I can do part a and part b correctly, but can't find do part C
    Really need help please!!!
    I can use the answer from part B but I can't see the connection between A and C and can't get the correct answer
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    (Original post by Oliviazh)
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    I can do part a and part b correctly, but can't find do part C
    Really need help please!!!
    I can use the answer from part B but I can't see the connection between A and C and can't get the correct answer
    Well you could just expand the quadratic and do 3 different sums. Can't go wrong with that.
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    i don't really think you need to use part a) for part c)

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    (Original post by the bear)
    i don't really think you need to use part a) for part c)

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    Just an off-topic question; why do you always put asterisks on everything you write?? lol
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    (Original post by RDKGames)
    Well you could just expand the quadratic and do 3 different sums. Can't go wrong with that.
    Well I did that but still wrong answer...must be something wrong with the calculation
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    (Original post by Oliviazh)
    Well I did that but still wrong answer...must be something wrong with the calculation
    Why are you using a calculator?? I mean, you're allowed yeah, but for what? There's nothing to calculate. You're probably factoring wrong. Show your working if you get stuck

    (2r-1)^2=4r^2-4r+1

    So \displaystyle \sum_{r=1}^{n} (4r^2-4r+1) = \sum_{r=1}^n (4r^2) + \sum_{r=1}^{n} (-4r) + \sum_{r=1}^{n} (1)

    The first term you can say that 4r^2=(2r)^2 and use the result from part b.
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    (Original post by RDKGames)
    Why are you using a calculator?? I mean, you're allowed yeah, but for what? There's nothing to calculate.

    (2r-1)^2=4r^2-4r+1

    So \displaystyle \sum_{r=1}^{n} (4r^2-4r+1) = \sum_{r=1}^n (4r^2) + \sum_{r=1}^{n} (-4r) + \sum_{r=1}^{n} (1)

    The first term you can say that 4r^2=(2r)^2 and use the result above.
    Um..I didn't use a calculator...I mean there must be something wrong with my calculation😂
    Just a quick question, for the last term in your equation, does the result of that part equal to 1 or n?
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    (Original post by Oliviazh)
    Um..I didn't use a calculator...I mean there must be something wrong with my calculation😂
    Just a quick question, for the last term in your equation, does the result of that part equal to 1 or n?
    Misread but there's still no calculation anyway lol. And yes. You are summing up 1 and n amount of times so it's 1*n hence n.
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    (Original post by RDKGames)
    Yes. You are summing up 1 and n amount of times so it's 1*n hence n.
    Thank you😃
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    Meh, the above is overkill.

    Better to think of it as summing the odd terms up till 2n-1, you know the sum of all terns from 1 to 2n and you know the sum of even terms from 1 to 2n. So the sum of all terms - sum of even terms (i.e: part a - part b) gets you what you want.
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    (Original post by RDKGames)
    Just an off-topic question; why do you always put asterisks on everything you write?? lol
    i don't.... it's some kind of bug which afflicts people with 12 gems ?

    the TSR techies are baffled

    :teehee: *
 
 
 
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