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Homework Help: Sum of arithmetic series

  1. Dec 11, 2009 #1
    1. The problem statement, all variables and given/known data

    The sum of the first 4 terms in an arithmetic series is -8 and the sum of the first 5 terms is 85. Determine the first term and the common difference.

    2. Relevant equations

    tn = a + (n-1)d
    Sn = n/2 (2a + (n-1)d)

    3. The attempt at a solution
     
  2. jcsd
  3. Dec 11, 2009 #2

    rock.freak667

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    Homework Helper

    I think you forgot to type in this section.
     
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