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# Need help on an arithmetic progression problem! watch

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1. 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.
2. Sum from 1 to 2n minus the sum from 1 to n+2.
What's the sum of the the first n integers?
3. 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}
4. (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?
5. (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
6. (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
7. (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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