Question 1158910
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If you don't know the formula for the sum of an arithmetic progression,

you have a happy opportunity to learn it from the lessons


&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/Arithmetic-progressions.lesson>Arithmetic progressions</A>

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/The-proofs-of-the-formulas-for-arithmetic-progressions.lesson>The proofs of the formulas for arithmetic progressions</A> 


in this site &nbsp;(on the free of charge basis).


If, &nbsp;in opposite, &nbsp;you DO know this formula, &nbsp;then do this job on your own.