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Homework Help: Arithmetic series

  1. Mar 10, 2009 #1
    1. The problem statement, all variables and given/known data

    The nth term of an arithmetic series is 1/2(3-n). What are the first three terms and the 20th term?

    2. Relevant equations

    nth term = a+(n-1)d

    3. The attempt at a solution

    I have made various attempts but cannot seem to work out how this can be done without a specific number for n. Have answered questions where two different terms have been given and used simultaneous equations to determine the first term and common difference but can't seem to do this as only one term is given. Advice anyone??
  2. jcsd
  3. Mar 10, 2009 #2


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    Hi kwuk! :smile:

    (i assume you mean (3-n)/2)

    erm :redface: … the first three terms have n = 1, 2, 3, and the 20th has n = 20 :wink:
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