Writting Expressions for Patterns

[vobotvixy]

1280, 640, 320, 160.....
Pattern Rule: start with 1280 and divide by 2 each time.
But I also have to write an algerbric expression and I'm not sure how to do that for division patterns.

Plz help thx

 

[pka]

1280, 640, 320, 160.....
Pattern Rule: start with 1280 and divide by 2 each time.
But I also have to write an algerbric expression and I'm not sure how to do that for division patterns.

Is this what you mean?
$\displaystyle a_n=\dfrac{1280}{2^{n-1}}$

 

[HallsofIvy]

You keep dividing by 2 and that "n-1" in pka's formula is the number of times you have divided by 2. For $\displaystyle a_1$, n= 1 and you divide 1280 by 2 1- 1= 0 times:$\displaystyle \frac{1280}{2^0}= \frac{1280}{1}= 1280$. For $\displaystyle a_2$, n= 2 and you divide 1280 by 2 2- 1= 1 times: $\displaystyle \frac{1280}{2^1}= \frac{1280}{2}= 640$, etc.