# Homework Help: Geometric series. Find the sum of the series. Powers.

1. Sep 13, 2010

### NotaPhysicist

1. The problem statement, all variables and given/known data

Find the sum of 9 terms of the series 3 + 3^(4/3) + 3^(5/3) + ...

2. Relevant equations

I'm just learning sequences and series and senior high school level. I'm finding it hard to apply a, ar, ar^(n-1), ... to this.

a = 3.

I don't know how to find common ratio. I'm confused. Once I know r I can apply the standard formula for summing the series.

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Any help will be greatly appreciated.

2. Sep 13, 2010

### VietDao29

In geometric series, the following term is obtained by multiplying the previous term by the common ratio r. Which, in turn, means that, you can obtain r by dividing the following term by the previous term; like this:

$$r = \frac{a_2}{a_1} = \frac{a_3}{a_2} = ... = \frac{a_n}{a_{n - 1}}$$

So, can you calculate the common ratio in the problem above?

3. Sep 13, 2010

### NotaPhysicist

Yes! I got it now. Thanks for your help!