# Math Help - How to find r for a GP summation?

1. ## How to find r for a GP summation?

Hi

Given such an equation, how do I find r? Thank you

(1-r^m)/ (1-r)= s
where m can be any positive whole number
s can also be any positive number

The equation is actually the summation for a GP series with a=1, so basically I want to know how to find r (ratio factor) for the sum of a GP .

2. ## Re: How to find r for a GP summation?

Maybe I'm wrong but it seems that something is missing from your formula, which you are supposed to use

S= [ A (r ^n - 1 ) ]/ r - 1 = ( A - r An ) /(1 - r) , where r = A2/A1 = A3/A2 = An + 1/An,

cheers