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Math Help - question

  1. #1
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    question

    f(x) is a continous function in R.
    i need to prove that if f(x)>=x2 for every x at R, so f(X) gets a minimum at [0,infinty).

    thanks!
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  2. #2
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    Re: question

    Quote Originally Posted by orir View Post
    f(x) is a continous function in R.
    i need to prove that if f(x)>=x2 for every x at R, so f(X) gets a minimum at [0,infinty).

    It is not true: f(x) = \left\{ {\begin{array}{*{20}{rl}}  {1,}&{\left| x \right| \leqslant 1} \\  {\left| {{x^3}} \right|,}&\text{else} \end{array}} \right.
    Last edited by Plato; April 9th 2013 at 03:17 PM.
    Thanks from topsquark
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  3. #3
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    Re: question

    but isn't it still a minimum?
    after all, still f(x0)<=f(x) [for every x at [0,infinity)]

    or not?
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  4. #4
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    Re: question

    Quote Originally Posted by orir View Post
    but isn't it still a minimum?
    after all, still f(x0)<=f(x) [for every x at [0,infinity)]

    Again, this may be a translation difficulty.
    What does "f(X) gets a minimum at [0,infinty)" mean?

    The function I gave you does have a minimum at every point in [-1,1], but on others.
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