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Math Help - Domain question...

  1. #1
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    Domain question...

    I'm having problems finding the domain of f(x) = ln(4 + ln(x)).

    I thought the domain of ln(x) was (0,infinity) but I was wrong.

    Can anyone explain how to find the domain of ln(x)?
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  2. #2
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    Quote Originally Posted by Ferny84 View Post
    I'm having problems finding the domain of f(x) = ln(4 + ln(x)).

    I thought the domain of ln(x) was (0,infinity) but I was wrong.

    Can anyone explain how to find the domain of ln(x)?
    Well, isn't it the case that e^y will ALWAYS be positive?
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  3. #3
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    Quote Originally Posted by Ferny84 View Post
    I'm having problems finding the domain of f(x) = ln(4 + ln(x)).

    I thought the domain of ln(x) was (0,infinity) but I was wrong.
    If, by that, you mean x positive, you are right. What makes you think you are wrong?

    But, of course, the domain of ln(x) is not necessarily the same as the domain of ln(4+ ln(x)). In order to be able to take the second logarithm, you must have 4+ ln(x)> 0 or ln(x)> -4. For what value of x is ln(x)= -4?

    Can anyone explain how to find the domain of ln(x)?
    You already know that. That's the wrong question!
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