Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    I need to rearrange this equation to find 'r' but I'm finding it a bit hard...

    8 = 3/1-r


    Also, there is a question which asks "A geometric series has first term 54 an 4th term 2. What is its common ratio?"

    Thanks.
    Offline

    16
    ReputationRep:
    kwalia.

    So what do you get if we multiply both sides of the equation by 1-r?

    a geometric series has first term 54 and 4th term 2.

    So we have that a=54 and that ar^3=2 can you solve this?
    • Thread Starter
    Offline

    0
    ReputationRep:
    I dont know, thats why im stuck...
    Offline

    0
    ReputationRep:
    8=3/(1-r), with r different of 1

    Multiply each side by (1-r)
    you get 8(1-r) = 3(1-r) / (1-r)

    On the RHS, the (1-r) cancels out

    Develop the LHS, and you get 8-8r=3, so 8r=5 so r=5/8
    Offline

    0
    ReputationRep:
    And for your second question, your notations are quite confusing, but basically, if
    a=54
    a*r^3 = 2,

    then you have r^3=2/a = 1/27
    so r= cube root (1/27)

    You know that 3^3 = 27 (or you find it)
    Therefore, r=1/3
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 7, 2010
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

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.