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Math Help - H/W Question.

  1. #1
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    H/W Question.

    Show that there is a real number x such that cos(x)=ln(x).


    Cheers.
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  2. #2
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    Quote Originally Posted by ardam View Post
    Show that there is a real number x such that cos(x)=ln(x).
    If f(x)=\ln(x)-\cos(x) then f(1)=?~\&~f(\pi)=?
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  3. #3
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    Quote Originally Posted by Plato View Post
    If f(x)=\ln(x)-\cos(x) then f(1)=?~\&~f(\pi)=?
    Then f(1) = -cos(1) = -0.9998476952

    And f(pi)= 0.146232736
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  4. #4
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    Quote Originally Posted by ardam View Post
    Then f(1) = -cos(1) = -0.9998476952

    And f(pi)= 0.146232736
    Well what does that imply?
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  5. #5
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    Quote Originally Posted by Plato View Post
    Well what does that imply?
    Sorry but im not sure.

    Could it be that x is between the values 1 and pi?
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  6. #6
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    Quote Originally Posted by ardam View Post
    Sorry but im not sure.
    What level of mathematics are you doing?
    You posted this question in an advanced forum.
    You should know the basic tools at this level.

    Have you heard of the Intermediate Value Theorem?
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