Proving that f is bounded on R

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SUMMARY

The discussion centers on proving that a continuous function f: R -> R, which approaches zero as x approaches both positive and negative infinity, is bounded on the entire real line R. The proof leverages the established fact that continuous functions are bounded on closed intervals [a, b]. By demonstrating that f is bounded on intervals of the form [b, +∞) and (-∞, a], the conclusion follows that f is bounded on all of R using compact intervals.

PREREQUISITES
  • Understanding of limits, specifically lim (x -> ∞)(f(x)) = 0
  • Knowledge of continuity and its implications for functions on closed intervals
  • Familiarity with the concept of compactness in real analysis
  • Experience with proofs in real analysis, particularly regarding boundedness
NEXT STEPS
  • Study the properties of continuous functions on closed intervals, focusing on the Heine-Borel theorem
  • Learn about the implications of limits at infinity for function behavior
  • Explore the concept of compact sets in real analysis and their significance
  • Review proof techniques in real analysis, particularly for establishing boundedness
USEFUL FOR

This discussion is beneficial for students of real analysis, mathematicians focusing on function properties, and educators preparing materials on continuity and boundedness in calculus.

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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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but I can't just assume it is that specific function surely? plus i have to prove it's bounded, not unbounded?!?
 
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.
 

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