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anonymous
 one year ago
What is the sum of the first 19 terms of an arithmetic series with a rate of increase of 7 and a7 = 46?
1,197
1,273
1,373
1,423
1,327
anonymous
 one year ago
What is the sum of the first 19 terms of an arithmetic series with a rate of increase of 7 and a7 = 46? 1,197 1,273 1,373 1,423 1,327

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anonymous
 one year ago
Best ResponseYou've already chosen the best response.0http://openstudy.com/study#/updates/51e54249e4b08833fb236305

Michele_Laino
 one year ago
Best ResponseYou've already chosen the best response.1since the general formula for the nth term is: \[\Large {a_n} = {a_1} + \left( {n  1} \right)d\] where d is constant of your sequance, namely d=7, then we can write: \[\Large \begin{gathered} {a_7} = {a_1} + \left( {7  1} \right) \times 7 \hfill \\ \hfill \\ 46 = {a_1} + \left( {7  1} \right) \times 7 \hfill \\ \end{gathered} \] please solve for a_1

Michele_Laino
 one year ago
Best ResponseYou've already chosen the best response.1hint: \[\Large 46 = {a_1} + 42\]

Michele_Laino
 one year ago
Best ResponseYou've already chosen the best response.1after that we have to compute a_19, using the same general formula above: \[\Large {a_n} = {a_1} + \left( {n  1} \right)d\] so we have: \[\Large {a_{19}} = {a_1} + \left( {19  1} \right) \times 7 = ...?\]

Michele_Laino
 one year ago
Best ResponseYou've already chosen the best response.1then the requested sum S is given by the subsequent formula: \[\Large S = \frac{{{a_1} + {a_{19}}}}{2} \times 19 = ...?\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0I got it!! Thank you!
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