Hey there! Sign in to join this conversationNew here? Join for free
 You are Here: Home >< A-levels

# Tricky geometric series question watch

1. Hi. I just completed a C2 mock today, and I thought I was pretty confident in geometric series...until I got this question. (not exact, I'm paraphrasing)

The sum of the first 2 terms in a geometric series with all positive terms is 32 and the sum to infinity is 164.
I) Find the common ratio
II) Find the first term.

The second part I know how to do, IF I could figure out the common ration. The problem is I keep getting weird equations like r-1=32a and a=162-162.

Any help would be appreciated, thanks.
2. We know:

and

Then by some rearranging:

and

Equate those two to each other and you should find r

(I think some of these equations might not render properly; sorry, I don't really know TSR-specific Latex formatting!

Reply
Submit reply
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 14, 2016
Today on TSR

### Struggling to get going with your revision?

Get going with the all day revision thread

### Uni strikes! How do they affect you?

Discussions on TSR

• Latest
Poll
Help with your A-levels

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Uni match

Our tool will help you find the perfect course for you

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Degrees without fees

Discover more about degree-level apprenticeships.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets

## Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

## Sponsored content:

### HEAR

Find out how a Higher Education Achievement Report can help you prove your achievements.

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.