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Logarithm equation

  1. Feb 5, 2013 #1
    1. The problem statement, all variables and given/known data
    3x + 3x+1 = 4x

    Can I do this ?

    Log 3x + Log 3x+1 = Log4x

    thanks
     
  2. jcsd
  3. Feb 5, 2013 #2

    micromass

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    No, you can't. The law

    [tex]\log(a+b)=\log(a)+\log(b)[/tex]

    is not valid.
     
  4. Feb 5, 2013 #3

    Dick

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    Absolutely not. log(3^x)+log(3^(x+1))=log(3^x*3^(x+1)), not log(3^x+3^(x+1)).
     
  5. Feb 5, 2013 #4
    How can I solve my equation ?
     
  6. Feb 5, 2013 #5

    tiny-tim

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    hi scientifico! :smile:
    no!!

    log(a + b) is not loga + logb !​

    hint: factorise 3x + 3x+1 :wink:
     
  7. Feb 5, 2013 #6

    Dick

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    3^(x+1)=3*3^x. Try using that.
     
  8. Feb 5, 2013 #7
    Thanks I solved.
     
  9. Feb 5, 2013 #8
    3(1-3^x) < 5^x(1-3^x)

    must I impose 1-3^x > 0 and 1-3^x < 0 ?
     
  10. Feb 5, 2013 #9

    micromass

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    Please post new questions in a separate thread.
     
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