Results 1 to 4 of 4

Math Help - Logarithm question [won't take two seconds!]

  1. #1
    Member
    Joined
    Oct 2008
    Posts
    157

    Logarithm question [won't take two seconds!]

    The question asks to solve

     log_a (3x + 4) - log_a x = 3 log_a 2

    I have got to

     log_a \frac{3x + 4}{x} = log_a 8

    But I'm not sure if this is the correct method or what to do after this to solve it.

    Could someone please help with this?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Nov 2008
    From
    France
    Posts
    1,458
    Hi

    I would advise first to find the domain of log_a (3x + 4) - log_a x = 3 log_a 2

    3x + 4 > 0 and x > 0 therefore x > 0

    Then OK for your method which leads to \frac{3x + 4}{x} = 8

    Solve for x and do not forget to check if x > 0
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Oct 2008
    Posts
    157
    Quote Originally Posted by running-gag View Post
    Hi

    I would advise first to find the domain of log_a (3x + 4) - log_a x = 3 log_a 2

    3x + 4 > 0 and x > 0 therefore x > 0

    Then OK for your method which leads to \frac{3x + 4}{x} = 8

    Solve for x and do not forget to check if x > 0
    I got 0.8 for x because I realized just now the method I needed! Thanks for helping.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Nov 2008
    From
    France
    Posts
    1,458
    Quote Originally Posted by db5vry View Post
    I got 0.8 for x because I realized just now the method I needed! Thanks for helping.
    That's it
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Centimetres into Seconds
    Posted in the Algebra Forum
    Replies: 3
    Last Post: May 27th 2011, 04:24 AM
  2. desperate seconds
    Posted in the Differential Equations Forum
    Replies: 20
    Last Post: December 17th 2010, 05:48 PM
  3. Division by 9 in five seconds!!!
    Posted in the Number Theory Forum
    Replies: 1
    Last Post: October 3rd 2009, 12:31 PM
  4. Find t (in seconds)
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: August 4th 2008, 05:21 AM
  5. minutes and seconds
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: June 29th 2008, 08:25 PM

Search Tags


/mathhelpforum @mathhelpforum