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Algebraic Expression

  • Thread starter Natko
  • Start date
  • #1
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Homework Statement



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

Homework Equations



t= term number

The Attempt at a Solution



no idea
 

Answers and Replies

  • #2
What do you multiply each term by to get the next?
 
  • #3
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What do you multiply each term by to get the next?
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.
 
  • #4
HallsofIvy
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Homework Helper
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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.
 
  • #5
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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.
So what would the algebraic expression to find the nth term be?
 

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