# Help find Sum

• Jul 28th 2008, 10:26 PM
helpless13
Help find Sum
find the sum of K 12-57

57
E(Sum) 7-4k
k=12 13
• Jul 28th 2008, 10:28 PM
Jhevon
Quote:

Originally Posted by helpless13
find the sum of K 12-57

57
E(Sum) 7-4k
k=12 13

i don't understand what you are trying to write. do you mean $\sum_{k = 12}^{57} \frac {7 - 4k}{13}$ ?
• Jul 28th 2008, 10:31 PM
helpless13
yes that's what i'm trying to write
• Jul 28th 2008, 10:31 PM
CaptainBlack
Quote:

Originally Posted by helpless13
find the sum of K 12-57

57
E(Sum) 7-4k
k=12 13

Would that be:

$
\sum_{k=12}^{57} \frac{7-4k}{13}
$

This is an arithmatic progression with first term $-\ \frac{41}{13}$ (which corresponds to $k=12$), common difference $-\ \frac{4}{13}$ and with $57-12+1 = 46$ terms. You should have a forumla for this.

RonL
• Jul 28th 2008, 10:35 PM
helpless13
I do have the formula I just cant get the write answer i dont know what im doing wrong
• Jul 28th 2008, 10:37 PM
helpless13
I know you have to take the sum of the first 57 terms and subtract the first 12 but i don't get the correct answer
• Jul 28th 2008, 10:42 PM
helpless13
Thanks
Alright thanks for your help i got it now