Proving that f is bounded on R

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In summary, the conversation is discussing how to prove that a continuous function f on R with limits approaching 0 from both positive and negative infinities is bounded on R. The suggestion is to first show that f is bounded on sets of the form [b,+\infty) and (-\infty,a] for some a, b, and then use the result for compact intervals [a,b] to complete the proof.
  • #1
vikkisut88
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Homework Statement


Suppose that f: R -> R is continuous on R and that lim (x -> [tex]\infty[/tex]+)(f(x) = 0) and lim (x -> [tex]\infty[/tex]-)(f(x)=0).
Prove that f is bounded on R


Homework Equations


I have got the proof of when f is continuous on [a,b] then f is bounded on[a,b] but I'm unsure as to whether I can use this proof for this particular question.

The Attempt at a Solution


My attempt is merely the proof I speak of from above.
 
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  • #2
but I can't just assume it is that specific function surely? plus i have to prove it's bounded, not unbounded?!?
 
  • #3
vikkisut88 said:

Homework Statement


Suppose that f: R -> R is continuous on R and that lim (x -> [tex]\infty[/tex]+)(f(x) = 0) and lim (x -> [tex]\infty[/tex]-)(f(x)=0).
Prove that f is bounded on R

Using the definitions of the above limits you should be able to show that f is bounded on sets of the form [b,+[tex]\infty[/tex]) and (-[tex]\infty[/tex],a] for some a, b.

vikkisut88 said:

Homework Equations


I have got the proof of when f is continuous on [a,b] then f is bounded on[a,b] but I'm unsure as to whether I can use this proof for this particular question.

Then use the result for compact intervals [a,b] to complete the proof that f is bounded on all of R.
 

What does it mean for a function to be bounded on R?

A function is considered bounded on the real numbers (denoted by R) if there exists a specific number M, such that the absolute value of the function's output is always less than or equal to M for all input values on the real number line. In other words, the function never reaches values that are infinitely large or small.

How do you prove that a function is bounded on R?

To prove that a function is bounded on R, you must show that there exists a specific value M that satisfies the definition of boundedness. This can be done by using various mathematical techniques, such as finding the maximum or minimum values of the function, or using the squeeze theorem.

What are the consequences of a function not being bounded on R?

If a function is not bounded on R, it means that there is no limit to how large or small the function's output can be. This can lead to problems in certain mathematical calculations and can make it difficult to make predictions based on the function's behavior.

Can a function be bounded on R but not on a specific interval?

Yes, it is possible for a function to be bounded overall on R, but not bounded on a specific interval within R. This means that while the function may have a limit on R, it may not have a limit on a smaller subset of R.

Are there different types of boundedness for functions on R?

Yes, there are different types of boundedness for functions on R. A function can be bounded above, meaning there is a maximum value for its output, or bounded below, meaning there is a minimum value for its output. Additionally, a function can be both bounded above and below, meaning there is both a maximum and minimum value for its output.

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