Help with integration proof with epsilon-delta

Lebesgue integration is being discussed and a proof by contradiction is being proposed to show that if f is continuous on [a,b] and the integral of the absolute value of f from a to b is equal to 0, then f(x) must be equal to 0 for all x in [a,b]. However, the conversation becomes confused about the details of the proof.
  • #1
Ara macao
27
0
Prove that if f is continuous on [a,b] and

[tex]\int_a^b |f(x)|\,dx = 0[/tex]

then f(x) = 0 for all x in [a,b].

so I'll have to use an epsilon delta proof by contradiction here. I'll have to assume that there exists a c such that f(c) != 0 and for all x = f(c)/2, there exists a delta such that |f(x)-f(c)|< epsilon for |x-c| < delta. and then I should make |f(x)| > epsilon /2. This would contradict the original hypothesis...

But I'm getting confused here...

Thanks!
 
Last edited:
Physics news on Phys.org
  • #2
Are you using Riemann integration or Lebesgue integration?
 
  • #3
Riemann integration
 

FAQ: Help with integration proof with epsilon-delta

What is epsilon-delta proof?

Epsilon-delta proof is a method used in mathematics to rigorously prove the limit of a function. It involves using two variables, epsilon (ε) and delta (δ), to show that for any arbitrarily small value of epsilon, there exists a corresponding value of delta that ensures the function will be within epsilon's distance from the limit.

Why is epsilon-delta proof important?

Epsilon-delta proof is important because it provides a rigorous way to prove the limit of a function. It is used in many areas of mathematics, including calculus and real analysis, to establish the convergence of a sequence or the continuity of a function. This method ensures that the limit is true for all possible values, not just a few examples.

How do you start an epsilon-delta proof?

The first step in an epsilon-delta proof is to write down the definition of the limit. This involves stating that for any arbitrarily small value of epsilon, there exists a corresponding value of delta that ensures the function will be within epsilon's distance from the limit. From there, you can use algebraic manipulations and logical reasoning to find a suitable value for delta.

What are common mistakes to avoid in an epsilon-delta proof?

One common mistake in an epsilon-delta proof is assuming that delta can be any value. Delta must be a specific value that depends on epsilon and the function at hand. Another mistake is using the same value for delta in different parts of the proof. Delta can vary depending on the input of the function, so it is important to use different values for different inputs.

Can epsilon-delta proof be used for all functions?

No, epsilon-delta proof can only be used for functions with well-defined limits. It cannot be used for functions with infinite limits or for functions that are discontinuous at the point in question. Additionally, the function must be defined for all values within a certain range, and the limit must exist at the point being considered.

Back
Top