Proving Boundedness of Continuous Functions in [a,+∞] with Limits

In summary, to prove that f(x) is bounded in [a, infinity) it is necessary to show that there is a limit as x goes to infinity and that f(x) is continuous on the interval [a, infinity). This can be done by choosing a suitable epsilon value and using the definition of limit at infinity. Additionally, since f(x) is continuous it is also bounded on a closed, bounded interval. By combining these two pieces of information, it can be concluded that f(x) is bounded.
  • #1
sedaw
62
0
need to prove that f(x) bounded if f(x) continuous in [a,+infinite] and if there's a limit while x goes to +infinite.


I would really appreciate any kind of help !
 
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  • #2
sedaw said:
need to prove that f(x) bounded if f(x) continuous in [a,+infinite] and if there's a limit while x goes to +infinite.


I would really appreciate any kind of help !

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.
 
  • #3
hello HallsofIvy ! , " I assume you mean prove that f is bounded in [a, infinity)."

that is right , i don't understand why did u choose epsilon=1 is it necessary ?

TNX!
 
  • #4
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?
 

1. What is a bounded function?

A bounded function is a mathematical function that is limited or confined within a certain range of values. This means that the output of the function will never exceed a certain value, regardless of the input.

2. How is a bounded function different from an unbounded function?

An unbounded function has no limitations on its output and can increase or decrease indefinitely. In contrast, a bounded function has a maximum or minimum value that it cannot exceed.

3. Why is it important to prove that a function is bounded?

Proving that a function is bounded is important because it allows us to understand the behavior of the function and make predictions about its output. It also helps us determine the domain and range of the function.

4. What are some common methods used to prove a function is bounded?

One common method is to use the definition of a bounded function, which states that for any input, the output must be within a certain range. Other methods include using calculus techniques such as the Extreme Value Theorem, or using the properties of limits.

5. Can a function be both bounded and unbounded?

No, a function cannot be both bounded and unbounded. It must fall into one of these two categories. However, it is possible for a function to be bounded on some intervals and unbounded on others.

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