# Algebraic Expression

1. Feb 5, 2012

### Natko

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. Feb 6, 2012

### DivisionByZro

What do you multiply each term by to get the next?

3. Feb 6, 2012

### Natko

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. Feb 6, 2012

### HallsofIvy

Staff Emeritus
Are you saying that you have a sequence, $a_1= -15$, $a_2= 30$, $a_3= 90$, and $a_4= -360$?

Well, I notice that 30= 2*15, 90= 3*30, and 360= 4*90. That is, $a_n= n*a_{n-1}$. Also, the signs are -, +, +, -. You should be able to find a power of -1, in terms of n, that will give that.

5. Feb 6, 2012

### Natko

So what would the algebraic expression to find the nth term be?