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Another log equation

  1. Nov 14, 2008 #1
    1. The problem statement, all variables and given/known data

    log x2 + log x - log 2.7 = log 10
    solve for x

    2. Relevant equations



    3. The attempt at a solution
    this one i really dont know how to do. I cant find any examples, but this is what i tried (youre gonna be like, what? but i had to attempt it.) I think when logs are in addition format, youre supposed to multiply them? does that make sense? i really need help on this one. :

    2 log x + log x = log 10 + log 2.7
    2 log x2 = log 27
    4 log x = log 27

    thats as far as i can get. i know its wrong. even one step in the right direction would help me.
     
  2. jcsd
  3. Nov 14, 2008 #2

    Dick

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    Science Advisor
    Homework Helper

    No, 2*log(x)+log(x) IS NOT 2*log(x^2). 2*log(x)+log(x)=3*log(x)=log(27). Try it from there. Or do log(x^2)+log(x)=log(x^3)=log(27).
     
    Last edited: Nov 14, 2008
  4. Nov 14, 2008 #3
    ^
    i had it that way the first time. i think i changed it because i got

    3 log x = log 27
    then to solve for x i got something that looks like this:

    x = log 27/3 log

    3 log? is it supposed to be 3 log 1?

    if so, the answer is 0. i put 0 on my exam, although i set it up incorrectly. my prof would give a point for the correct answer and i got no points, so i dont think thats the answer.
     
  5. Nov 14, 2008 #4

    Mark44

    Staff: Mentor

    "3 log" makes no sense. Go back a step to 3 log x = log 27.

    What's another way to write 3 log x?
     
  6. Nov 14, 2008 #5

    Dick

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    Science Advisor
    Homework Helper

    3*log(x)=log(x^3), doesn't it? 3log(x) is not 3*log*x. That's just plain silly, as Mark44 points out.
     
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