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Math Help - basic logarithm problem

  1. #1
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    basic logarithm problem

    Hi, I just don't get this sort of Logarithm problems that have same two variable in the equation.
    The problem is:
    Solve for x
    log x + log(x+3)=1


    thanks for the help =]
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  2. #2
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    Quote Originally Posted by cbbplanet View Post
    Hi, I just don't get this sort of Logarithm problems that have same two variable in the equation.
    The problem is:
    Solve for x
    log x + log(x+3)=1


    thanks for the help =]
    Rewrite using log properties

    Log(x(x+3))=1

    rewrite in expo form.

    x(x+3)=10 \iff x^2+3x-10=0

    (x-2)(x+5)=0

    So x=2 or x=-5

    But if you plug x=-5 into the original equation you end up with the log(-5)

    which is undefined. So the only solution is x=2.
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