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Algebraic Expression

  1. Feb 5, 2012 #1
    1. The problem statement, all variables and given/known data

    In this pattern, what is the algebraic expression for the term t?
    -15, 30, 90, -360

    2. Relevant equations

    t= term number

    3. The attempt at a solution

    no idea
     
  2. jcsd
  3. Feb 6, 2012 #2
    What do you multiply each term by to get the next?
     
  4. Feb 6, 2012 #3
    That's what I want to find out. It does not necessarily have to be multiplication only.

    In words it would be:
    current term value = the previous term's value multiplied by the current term number, and change poles if the current term number is even; the first term value is -15.
     
  5. Feb 6, 2012 #4

    HallsofIvy

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    Science Advisor

    Are you saying that you have a sequence, [itex]a_1= -15[/itex], [itex]a_2= 30[/itex], [itex]a_3= 90[/itex], and [itex]a_4= -360[/itex]?

    Well, I notice that 30= 2*15, 90= 3*30, and 360= 4*90. That is, [itex]a_n= n*a_{n-1}[/itex]. Also, the signs are -, +, +, -. You should be able to find a power of -1, in terms of n, that will give that.
     
  6. Feb 6, 2012 #5
    So what would the algebraic expression to find the nth term be?
     
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