Integral of a continuously differentiable function on [a,b].

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Discussion Overview

The discussion revolves around the integral of a continuously differentiable function on the interval [a,b], specifically focusing on the properties of the function f, where f(a)=f(b)=0 and the integral of f squared equals one. Participants are tasked with showing that the integral of the product of x, f(x), and f'(x) equals -1/2 over the interval [a,b]. The scope includes mathematical reasoning and integration techniques.

Discussion Character

  • Mathematical reasoning

Main Points Raised

  • One participant proposes to show that the integral of x, f(x), and f'(x) equals -1/2 over [a,b] given the conditions on f.
  • Another participant questions how to express the term f(x)f'(x), indicating a need for clarification on this product.
  • A third participant reiterates the initial problem and suggests using integration by parts, leading to a formulation involving the boundary terms and the integral of f squared.
  • A later reply seeks to elaborate on the integration by parts suggestion by asking for the derivative of (f(x))^2, which may relate to the earlier discussions on f(x) and f'(x).

Areas of Agreement / Disagreement

Participants appear to be exploring the problem collaboratively, but there is no consensus on the approach or resolution of the integral at this stage. Multiple viewpoints and methods are being discussed without a clear agreement.

Contextual Notes

Limitations include the dependence on the definitions of the functions involved and the unresolved steps in the integration process. The discussion does not clarify the assumptions behind the integration by parts method or the implications of the boundary conditions.

rsa58
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suppose f is real, continuously differentiable function on [a,b], f(a)=f(b)=0 and

integral f^2dx=1

show [integral(xf(x)f'(x)dx)= -1/2 over [a,b]
 
Last edited:
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How can you write the term f(x)\,f'(x)?
 
rsa58 said:
suppose f is real, continuously differentiable function on [a,b], f(a)=f(b)=0 and

integral f^2dx=1

show [integral(xf(x)f'(x)dx)= -1/2 over [a,b]
Integrate by parts:

You will get 1/2(bf2(b)-af2(a)-integral(a,b)f2(x))
 
Elaborating on Rainbow Child's suggestion, what is the derivative of (f(x))2?
 

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