Uniformly continuous and bounded

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SUMMARY

The discussion centers on proving that a uniformly continuous function f on a bounded set A in ℝ¹ is also bounded. The key argument presented is that for any ε > 0, there exists a δ > 0 such that the function's variation can be controlled by selecting a finite number of points in A. Specifically, the total variation of f over these intervals is limited to 2nε, demonstrating that f is indeed bounded on A.

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  • Understanding of uniformly continuous functions
  • Knowledge of bounded sets in real analysis
  • Familiarity with the concept of total variation
  • Basic proficiency in ε-δ definitions in calculus
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  • Explore the implications of boundedness in real analysis
  • Learn about total variation and its applications in function analysis
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math2006
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Let [tex]f[/tex] be a real uniformly continuous function on the bounded
set [tex]A[/tex] in [tex]\mathbb{R}^1[/tex]. Prove that [tex]f[/tex] is bounded
on [tex]A[/tex].

Since f is uniformly continuous, take [tex]\epsilon = m, \exists \delta > 0[/tex]
such that
[tex]|f(x)-f(p)| < \epsilon[/tex]
whenever [tex]|x-p|<\delta[/tex] and [tex]x,p \in A[/tex]
Now we have
[tex]|f(x)| < m + |f(p)|[/tex]

Obviously i should show [tex]b + |f(p)|[/tex] is bounded, but no idea how.
Could someone help me? thx
 
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math2006 said:
Obviously i should show [tex]b + |f(p)|[/tex] is bounded, but no idea how.
What is b? And why would you want to show that b + |f(p)| is bounded? You mean bounded as a function of p? Well that's no easier than showing directly that f is bounded, so this doesn't seem to be a worthwhile approach.

The idea is simple. Fix [itex]\epsilon > 0[/itex]. There exists [itex]\delta > 0[/itex] such that, well, you know. Since A is bounded, you can choose a FINITE number of points x1, ..., xn in A such that the intervals of radius [itex]\delta[/itex] about the xi cover A. The total variation of f on these intervals is at most [itex]2\epsilon[/itex], so the total variation of f over all of A is at most [itex]2n\epsilon[/itex].

Oh, and if this was homework, it should have been in the homework section.
 

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