# Math Help - C2 Geometric series help

1. ## C2 Geometric series help

Stuck here on the sufficient method to approach this question, would it involve using the a(1-r^n)/1-r formula? Any assistance would be greatly appreciated. Cheers.

'The sum of the first four terms of a geometric series is 5468.75 and the first term is 2000. Find the value of the common ratio and if all the terms are positive.'

2. ## Re: C2 Geometric series help

Originally Posted by DonGorgon
Stuck here on the sufficient method to approach this question, would it involve using the a(1-r^n)/1-r formula? Any assistance would be greatly appreciated.
'The sum of the first four terms of a geometric series is 5468.75 and the first term is 2000. Find the value of the common ratio and if all the terms are positive.'
You have all the parts, use them.
$5468.75=\frac{2000(1-r^4)}{1-r}$

3. ## Re: C2 Geometric series help

2000r^4 - 5468.75r 3468.75 = 0

Along the right lines?