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Need help on an arithmetic progression problem! watch

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    I'm kinda stuck on this question, I'm not really sure on how to approach it, I've gotten pretty much nowhere so far.
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    Sum from 1 to 2n minus the sum from 1 to n+2.
    What's the sum of the the first n integers?
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    the first term a is n+3

    there are 2n - ( n + 3 ) + 1 terms let us call this w

    do you know what is the difference d ?

    then use the formula Sw = w/2{2a + (w - 1) d}
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    (Original post by the bear)
    the first term a is n+3

    there are 2n - ( n + 3 ) + 1 terms let us call this w

    do you know what is the difference d ?

    then use the formula Sw = w/2{2a + (w - 1) d}
    How did you find the number of terms, where did the plus one come from?
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    (Original post by Samii123)
    How did you find the number of terms, where did the plus one come from?
    if the terms were numbered 4,5,6,7,8 then there are not ( 8 - 4 ) terms but ( 8 - 4 ) + 1
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    (Original post by the bear)
    if the terms were numbered 4,5,6,7,8 then there are not ( 8 - 4 ) terms but ( 8 - 4 ) + 1
    Ok, I've finally got it! Thank you so much for your help! It's just that I got confused with the last term of the series and the number of terms in the series.

    Edit: Arrrrrgh PRSOM
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    (Original post by Samii123)
    Ok, I've finally got it! Thank you so much for your help! It's just that I got confused with the last term of the series and the number of terms in the series.

    Edit: Arrrrrgh PRSOM
    don't worry we have all been there.
 
 
 
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