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Arithmetic Sequences and Series

  1. Jul 20, 2011 #1
    1. The problem statement, all variables and given/known data

    Just a quick question I was looking to have cross checked…

    Q. Find un, the nth term of sequence -5, 0, 5, 10,…


    2. Relevant equations

    un = a + (n-1)d

    3. The attempt at a solution

    -5 + (n-1)5
    -5 + 5n - 5
    5n-10

    The answer in the book, however, indicates that un = 5n. Am I wrong, or are they? Thanks.
     
  2. jcsd
  3. Jul 20, 2011 #2

    gb7nash

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    Homework Helper

    Depends. Are we assuming the first term has index 1? 0? -1? 1000?

    If the first term has index -1, then the book is right. Your answer is also right, but you want to state that the first term has index 1.
     
  4. Jul 20, 2011 #3
    I answered two other questions just like it, before this one, and had no problem getting the answer, although the first terms in both of those sequences were positive.

    Thanks for the tip, though. I'll mention the index when answering other questions like it in future.
     
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