Question 1175017
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For the formula, its derivation and its usage see 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.



It is about arithmetic progressions and their sums.


Read these lessons; if you want to get more fan, read other associated lessons

that are referred at the end of these two.



Happy learning (!)