Turn on thread page Beta
    • Thread Starter
    Offline

    9
    ReputationRep:
    Solve the equation: 2log5 (x) - log5 (3x) = 1

    am i supposed to factorise the x?
    x[2log5(1) - log5 (3)] = 1 ?

    or do i have to use the log laws? i'm confused because either way it doesn't seem to work
    • Community Assistant
    • Very Important Poster
    Offline

    20
    ReputationRep:
    Community Assistant
    Very Important Poster
    Use log laws to manipulate the LHS so that you have \log_5(\text{something})=1.
    Offline

    11
    ReputationRep:
    (Original post by sadboynerd)
    Solve the equation: 2log5 (x) - log5 (3x) = 1

    am i supposed to factorise the x?
    x[2log5(1) - log5 (3)] = 1 ?

    or do i have to use the log laws? i'm confused because either way it doesn't seem to work
    You can't do that, by factoring out a  x , you're implying that  \log (x) = x\log(1) which is not the case.  \log() is a function, whatever goes inside the brackets is called the 'argument' of the function.

    To prove to yourself that  \log(a) \not= a\log(1) , try some values for  a .

    Example: Taking  a = 5 , by your definition

     \log 5 = 5\log1

     \log 5  \approx 0.6987...

     5\log1 = 0

     \therefore \log 5 \not= 5\log1
    Offline

    9
    ReputationRep:
    (Original post by sadboynerd)
    Solve the equation: 2log5 (x) - log5 (3x) = 1

    am i supposed to factorise the x?
    x[2log5(1) - log5 (3)] = 1 ?

    or do i have to use the log laws? i'm confused because either way it doesn't seem to work
    are you sure it's not 2log5(x)-log5(3x)=-1? I got a solution but it only works for -1

    UPDATE: false alarm. I made a mistake. I found the solution. You need to rewrite the 1 as log5(5), move it to the other side of the equation to make it equal 0, and work from there. Feel free to ask in case any more help is needed.
    Offline

    18
    ReputationRep:
    (Original post by tim_72)
    are you sure it's not 2log5(x)-log5(3x)=-1? I got a solution but it only works for -1
    there is a solution to OPs equation, an integer one at that
    Offline

    9
    ReputationRep:
    (Original post by DylanJ42)
    there is a solution to OPs equation, an integer one at that
    yeah i made a mistake, i edited the reply. thanks though
    • Thread Starter
    Offline

    9
    ReputationRep:
    thank you all guys for the help i solved it!
    Offline

    9
    ReputationRep:
    (Original post by sadboynerd)
    thank you all guys for the help i solved it!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 6, 2017
Poll
Do you think parents should charge rent?
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.