F is integrable but f^2 is not integrable

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Homework Help Overview

The discussion revolves around finding an example of a sequence of integrable functions where a function \( f \) is integrable but \( f^2 \) is not. The specific function under consideration is \( f(x) = \frac{1}{\sqrt{x}} \) on the interval [0, 1].

Discussion Character

  • Exploratory, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the function \( f(x) = \frac{1}{\sqrt{x}} \) and its integrability, questioning whether it serves as a valid example. There are inquiries about the proof process for demonstrating the integrability of \( f \) and the non-integrability of \( f^2 \).

Discussion Status

Some participants express confidence that the chosen function works, while others seek clarification on the proof requirements and theorems related to integrability. There is an acknowledgment that proofs might not need to be overly complex.

Contextual Notes

Participants are considering the implications of improper integrals and the need for imagination in approaching the problem. There is mention of various theorems regarding integrability, but no specific theorem is identified as universally applicable.

pulin816
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Homework Statement



Give an example of a sequence of integrable functions f:R -> R such that f is integrable but f^2 is not integrable. Prove your results.


The Attempt at a Solution




would 1/sqrt(x) for x ∈ [0,1] work? any other suggestions?
how would you prove that its does work? would you just plug it in and show it doesn't work or is there something more to it?

Thanks! I really appreciate your help!
 
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Sure f(x)=1/sqrt(x) on [0,1] works. Just integrate it. It's improper, but that shouldn't be a problem.
 
super. I thought proofs had to be more complicated, somehow.
Is there any theorem that explains integrability?
 
pulin816 said:
super. I thought proofs had to be more complicated, somehow.
Is there any theorem that explains integrability?

There's a lot of theorems about integrability. There's no one that explains everything. If you can do it as an elementary integral, like this one, you don't need anything complicated. Just a little imagination.
 

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