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Homework Help: Bounded function prove

  1. Jan 3, 2009 #1
    need to prove that f(x) bounded if f(x) continuous in [a,+infinite] and if theres a limit while x goes to +infinite.


    I would really appreciate any kind of help !
     
    Last edited by a moderator: Jan 3, 2009
  2. jcsd
  3. Jan 3, 2009 #2

    HallsofIvy

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    I assume you mean prove that f is bounded in [a, infinity). Otherwise, it is not true. Let the limit be L. By definition of limit at infinity, that means that there exist some R such that if x> R, |f(x)- L|< 1 so for x> R, L-1< f(x)< L+1. Further since f(x) is continuous, f is bounded on the close, bounded interval [0, R]. Put those two together.
     
  4. Jan 4, 2009 #3
    hello HallsofIvy ! , " I assume you mean prove that f is bounded in [a, infinity)."

    that is right , i dont understand why did u choose epsilon=1 is it necessary ?

    TNX!!
     
  5. Jan 4, 2009 #4

    HallsofIvy

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    Since the problem is only to prove that f is bounded, you can choose [itex]\epsilon[/itex] to be any (non-zero) number. "1" happened to be convenient.

    If |f(x)|< B on [0, R] and |f(x)|< 1 on [R, infinity), what is a bound on f?
     
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