Results 1 to 4 of 4
Like Tree1Thanks
  • 1 Post By Plato

Thread: Exponential and Logarithmic Equations

  1. #1
    Member
    Joined
    May 2013
    From
    California
    Posts
    144
    Thanks
    7

    Exponential and Logarithmic Equations

    Hey guys,

    log(x+3) - logx = 1


    so I got 1 = (x+3) / (x)

    and the book says the answer is 1/3

    I don't know how it got this

    any help? Thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Apr 2005
    Posts
    19,781
    Thanks
    3030

    Re: Exponential and Logarithmic Equations

    Is that the common logarithm? Base 10? If so then you have $\displaystyle log(x+3)- log(x)= log\left(\frac{x+ 3}{x}\right)= 1$ and then "get rid of" the logarithm by taking 10 to the power of each side. Instead of getting $\displaystyle \frac{x+ 3}{x}= 1$ you should have $\displaystyle \frac{x+ 3}{x}= 10^1= 10$.

    Can you solve $\displaystyle \frac{x+ 3}{x}= 10$?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Aug 2006
    Posts
    21,782
    Thanks
    2824
    Awards
    1

    Re: Exponential and Logarithmic Equations

    Quote Originally Posted by Cake View Post
    log(x+3) - logx = 1
    and the book says the answer is 1/3 I don't know how it got this
    .


    The answer depends upon the base.

    If $\displaystyle {\log _b}(x + 3) - {\log _b}(x) = 1$ then $\displaystyle {\log _b}\left( {\frac{{x + 3}}{x}} \right) = 1$.

    Then $\displaystyle \frac{x+3}{x}=b$.

    So I don't know where that answer comes from.
    Thanks from Cake
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member
    Joined
    May 2013
    From
    California
    Posts
    144
    Thanks
    7

    Re: Exponential and Logarithmic Equations

    Correct, it is base 10. Ahh I see. So whenever I have " = 1 " and with a base of 10. It automatically equals to 10^1?

    and yes, thank you. That gives me 1 / 3. Thanks a lot for clearing this up. I would have never gotten this.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Exponential & Logarithmic Equations
    Posted in the Pre-Calculus Forum
    Replies: 5
    Last Post: Mar 14th 2013, 09:24 AM
  2. Exponential & Logarithmic Equations
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: Mar 14th 2013, 09:00 AM
  3. Exponential and Logarithmic Equations
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: Dec 14th 2009, 05:41 AM
  4. Exponential and Logarithmic Equations
    Posted in the Algebra Forum
    Replies: 6
    Last Post: Nov 23rd 2008, 02:11 PM
  5. Exponential and Logarithmic Equations
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: Jun 15th 2006, 12:08 PM

Search Tags


/mathhelpforum @mathhelpforum