Prove or disprove: Justify your answer using the def or limit. Real analysis

In summary, if a function f has a positive limit L at zero, then there exists a positive real number m such that for any value of x within the domain of f, if 0<|x|<m, then f(x)>0. This can be proven by using the definition of the limit of a function at a point and setting ε=L. By setting m=δ, it can be shown that for 0<|x|<m, f(x)>0.
  • #1
Hodgey8806
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3

Homework Statement


Suppose f: ℝ-{0} → ℝ has a positive limit L at zero. Then there exists m>0 such that if 0<|x|<m, then f(x)>0.

Homework Equations


The definition of the limit of a function at a point is: (already assuming f to be a function and c being a cluster point)
A real number L is said to be a limit of f at c if, given any ε>0, there exists a δ>0 such that if x is an element of the domain and 0<|x-c|< δ, then |f(x)-L|<ε.

The Attempt at a Solution


I'm proving this true as:
Spse the limit as x→0 of f = L (being a positive real number.
This implies that given ε>0, there exists δ>0 such that 0<|x-0|< δ, then |f(x) - L|<ε.
Let ε=L,
By definition of the limit of a function at a point there exiss δ>0 such that for x in ℝ - {0}, 0<|x|<δ and |f(x) - L|<L if and only if 0<f(x)<2L.
Thus taking m = δ, then for 0<|x|<m and f(x)>0.

I'm sure it is sloppy, but it does make sense to me here. Please, constructive criticism is welcome! :)
 
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  • #2
Makes sense to me.
 
  • #3
I agree this is actually quite well done.
 
  • #4
Thank you very much! Finally analysis is coming back around to itself so I can sort of see where things are going easier :)
 

FAQ: Prove or disprove: Justify your answer using the def or limit. Real analysis

1. What is the definition of "prove" in real analysis?

In real analysis, "prove" refers to the process of providing a rigorous, logical argument or mathematical demonstration that a statement or theorem is true.

2. How is "disprove" different from "prove" in real analysis?

"Disprove" in real analysis refers to the process of providing a counterexample or logical argument that shows a statement or theorem is false. Unlike proving, disproving does not necessarily require a rigorous mathematical proof, but rather a single counterexample is sufficient to show that a statement is false.

3. What is the role of justification in proving or disproving in real analysis?

Justification is an essential aspect of proving or disproving in real analysis. It involves providing logical reasoning and mathematical evidence to support a claim or argument. Without proper justification, a proof or disproof is not considered valid in real analysis.

4. How does the concept of limit relate to proving or disproving in real analysis?

The concept of limit is crucial in real analysis as it allows us to rigorously define and analyze the behavior of functions and sequences. In proving or disproving, the limit can be used to provide evidence for or against a statement, as it helps to establish the behavior of a function or sequence in a given context.

5. What is the importance of using the definitions in real analysis when proving or disproving?

In real analysis, definitions serve as the foundation for all mathematical arguments and proofs. They provide precise and unambiguous descriptions of mathematical concepts, allowing for rigorous reasoning and logical arguments. When proving or disproving, it is crucial to use the definitions accurately and carefully to ensure the validity of the argument.

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