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I need help with an FP1 series question!! watch

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    i am following the Heinemann FP1 book, and in chapter 2 (Series), i had no problem with exercise 2a (about using identities to find expressions for the sum of series), but there are many in exercise 2b ("Summation of finite series") which i dont know how to do...

    you are supposed to use the established formulae for the sum of
    r2, r3, r(r+1) etc...

    for example,

    find the sum (from r=1 to 20) of 1/r(r+3)(r+6) or 1/r(r+1)

    THANX A LOT!!
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    Do you know about partial fractions? If so, use them.
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    is that what you're supposed to use?? because there is no mention or explanation of it in the book

    so you have to write the expression in partial fractions (using the A, B and C thing), then substitute in values... see which cancel...

    write the final expression and then substitute for the n?? (if it doesn't start at r=1, can you simply subtract the top from the bottom and add 1 and use this number??)
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    Write it in partial fractions, then write out some terms of the sum (the first few terms and the last few terms). You should see that many will cancel quite nicely, so the final answer is quite neat.

    I'm being deliberately vague here - I can be more specific if you get stuck in your working. Go for the partial fractions first.
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    (Original post by Markos258)
    is that what you're supposed to use?? because there is no mention or explanation of it in the book

    so you have to write the expression in partial fractions (using the A, B and C thing), then substitute in values... see which cancel...

    write the final expression and then substitute for the n?? (if it doesn't start at r=1, can you simply subtract the top from the bottom and add 1 and use this number??)
    If it does not start at r=1 then do from 1 to n and take away sum from 1 to 4 . (If it is from 5 to n)
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    ok... i understand it perfectly know ... thanx to both of you!!

    CHAPTER 1 (Inequalities) and CHAPTER 2 (Series) completed

    i'm doing AS Further Maths self-study and this summer i'm doing M2 and FP1 ... its not being TOO HARD (until now at least) ...

    if i have any more questions... i'll know where to ask THANXX!!
 
 
 
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Updated: July 9, 2006

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