Very Simple Question, : Integral of a derivative squared

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    Derivative Integral
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Discussion Overview

The discussion revolves around the integration of the square of a derivative, specifically the integral of \((\frac{dx}{dt})^{2}dt\). Participants explore methods for integration, including integration by parts, while addressing the challenge posed by the lack of an explicit function \(x(t)\).

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Homework-related, Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about how to integrate \(\int(\frac{dx}{dt})^{2}dt\).
  • Another suggests that partial integration might be applicable.
  • A participant notes that \(x\) must be defined in terms of \(t\) to proceed with the integration.
  • There is a question about whether \(x(t)\) is explicitly known, which is confirmed to be unknown by another participant.
  • A participant mentions that integration by parts could be used, but questions the existence of an elementary anti-derivative for \((\frac{dx}{dt})^{2}\).
  • Another participant provides a formula resulting from integration by parts, indicating a more complex relationship involving \(x\), \(x'\), and \(x''\).
  • One participant reflects on a misconception regarding the equivalence of \(\int(dx/dt)dt\) and \(x\), acknowledging the complexity of the problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the integration method or the existence of a simple solution, indicating multiple competing views and unresolved questions.

Contextual Notes

The discussion highlights the dependence on the definition of \(x(t)\) and the potential complexity of the integral, with participants noting that the lack of an explicit function complicates the integration process.

gilgtc
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Hello,

I am trying to figure out how to integrate this, I know it must be simple but I am not sure how to do it.

[tex]\int(\frac{dx}{dt})^{2}dt[/tex]


Thanks a lot!
 
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I think partial integration can work.
 
You just need x defined in terms of t

x = x(t)

then you can differentiate with respect to t,

then you square dx/dt

then you integrate that across t from t1 to t2

right?
 
Last edited:
Wait a second is x(t) explicitly known?
 
hi, thanks for your answers. x(t) is not known that is why I am not sure how to do it. Otherwise what Nick mentioned would be easily applicable.

Any other ideas? What do you mean by partial integration dirk_mec1?

Thanks!
 
He means "integration by parts". Do you have any reason to think that there is any simple answer to this question? I can see no reason to assume that
[tex]\right(\frac{dx}{dt}\)^2[/tex]
even has an elementary anti-derivative.
 
I don't think you can just integrate [tex]\int (f'(x))^2 \mbox{d}x[/tex], right? The integration by parts(thanks hallsofIvy ) however gives:

[tex]x (x'(t))^2 - \int x \cdot 2x' \cdot x''\ \mbox{d}t[/tex]
 
Last edited:
re

I thought that there was an easy equivalence like:

[tex]\int(dx/dt)dt = x[/tex]

I guess not! thanks for your help in any case.
 

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