Solving Integration Question: f' Continuous on [a,b]

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Discussion Overview

The discussion revolves around a mathematical problem involving the integration of a function \( f \) whose derivative \( f' \) is continuous on the interval \([a,b]\). Participants are tasked with showing that the integral \(\int_a^{b} f(t)f’(t) dt\) equals \(\frac{1}{2} [f^2(b) - f^2(a)]\), with hints provided for approaching the solution.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty with the integration question and seeks assistance.
  • Another participant questions whether the terms on the right-hand side of the equation are second derivatives or squares, suggesting an alternative expression involving \( f(b)^2 - f(a)^2 \).
  • A different participant asserts that the terms are indeed squares and provides reasoning based on notation conventions for derivatives.
  • Another participant proposes using integration by parts as a potential method to solve the problem.
  • There is a request for clarification on how to arrive at the proposed answer, indicating confusion about the reasoning behind it.

Areas of Agreement / Disagreement

Participants show disagreement regarding the interpretation of the terms on the right-hand side of the equation, with some believing they represent second derivatives while others assert they are squares. The discussion remains unresolved as multiple competing views are presented.

Contextual Notes

There are indications of confusion regarding notation and the interpretation of mathematical expressions, particularly concerning the distinction between derivatives and squares. The discussion also reflects varying levels of understanding among participants.

Who May Find This Useful

Students and individuals seeking assistance with integration techniques, particularly in the context of calculus and mathematical reasoning, may find this discussion relevant.

trap
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I'm having major trouble with this question, can anyone assist me on this?

Let f be a function such that f' is continuous on [a,b]. Show that

[tex]\int_a^{b}[/tex] f(t)f’(t) dt = 1/2 [f''(b) - f''(a)]

Hint: Calculate the derivative of F(x) = f''(x).
 
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Don't double post please
 
sorry, i thought a different forum would make a difference, since no one has an answer to my question yet.
 
trap said:
sorry, i thought a different forum would make a difference, since no one has an answer to my question yet.
Have you not read your other thread? People have been quite helpful.
 
Hi, are you sure those are second derivatives on the right hand side and not squares? Something like [tex]1/2(f(b)^2-f(a)^2)[/tex] instead?
 
i'm not sure if they are squares becoz the question reads f^2(b) - f^2(a)..so i thought they were second derivative..
 
trap said:
i'm not sure if they are squares becoz the question reads f^2(b) - f^2(a)..so i thought they were second derivative..
That is squares and I am sure about that because it is the answer. When your talking about the nth derivative you either use roman numerals or put the number in brackets.
 
Couldn't one simply integrate by parts to get the answer?
 
shmoe said:
Hi, are you sure those are second derivatives on the right hand side and not squares? Something like [tex]1/2(f(b)^2-f(a)^2)[/tex] instead?
Could you please explain how you come to that answer, I am having trouble seeing it.

Thanks.
 
  • #10
digink said:
Could you please explain how you come to that answer, I am having trouble seeing it.

Thanks.

Just use the hint applied to [tex]F(x)=(f(x))^2[/tex]. Find the derivative of F(x) using the chain rule...


DeadWolfe-yes integration by parts will work fine.
 

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