Can anyone explain to me what this is asking/how to do this? I think it's for the summation formula
et/?f=S_%7Bn%7D%20%3Dn%28%5Cfrac%7Ba_%7B1%7D%2Ba_%7Bn%7D%20%20%7D%7B2%7D%29" id="TexFormula1" title="S_{n} =n(\frac{a_{1}+a_{n} }{2})" alt="S_{n} =n(\frac{a_{1}+a_{n} }{2})" align="absmiddle" class="latex-formula"> but if I'm given a1, an, and n, what are the other numbers for?
This question is asking for the sum of all the terms in an arithmetic series.
So using the formula : Sn = n/2 (a+l) , where Sn is the sum of n terms, a is first term, and l is last term, we try to find Sn, with n being 25, a being 20, and an which is a25 or the twenty fifth term being 260, also being the last term.
Hence we can produce the formula for Sn which is Sn=25/2 (20+260)
