What has been done here to simplify the integration

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    Integration Simplify
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Discussion Overview

The discussion revolves around the integration of the expression involving $e^{-st}$, specifically focusing on the methods used to simplify the integration process. Participants explore the application of integration techniques, including integration by parts and alternative approaches suggested by a lecturer.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the lecturer's manipulation of $e^{-st}$, noting the equivalence of rewriting it as $\frac{d}{dt}e^{-st}$ and questioning the subsequent steps.
  • Another participant suggests that the lecturer applied the 'integration by parts' rule, which is a standard method for such integrals.
  • A participant acknowledges a misunderstanding and reflects on the lecturer's mention of a 'trick' to integrate without using integration by parts.
  • Another participant reinforces the idea that integration by parts is a common approach and suggests that tabular integration could be an alternative, though it may not be necessary for a single application.
  • One participant clarifies that the first step in the integration relies on the derivative relationship $\frac{d(e^{-st})}{dt} = -s e^{-st}$, allowing for the factor $-\frac{1}{s}$ to be taken out of the integral.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the method of integration, with some supporting the use of integration by parts while others mention alternative approaches. The discussion remains unresolved regarding the specific 'trick' referenced by the lecturer.

Contextual Notes

Some participants express uncertainty about the steps involved in the integration process and the implications of the lecturer's methods. There is a lack of clarity on the alternative integration technique mentioned.

nacho-man
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Please refer to the attached image.

My lecturer seems to have re-written $e^{-st}$ as $\frac{d}{dt}e^{-st}$ and taken out the $(-\frac{1}{s}$ which I do see is equivalent, but i am unsure how he goes from there onwards.

Although, e is the derivative of itself. how does he split the integral into two, despite there being a multiplication of the terms?
 

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nacho said:
Please refer to the attached image.

My lecturer seems to have re-written $e^{-st}$ as $\frac{d}{dt}e^{-st}$ and taken out the $(-\frac{1}{s}$ which I do see is equivalent, but i am unsure how he goes from there onwards.

Although, e is the derivative of itself. how does he split the integral into two, despite there being a multiplication of the terms?

Your lecturer has applied the 'integration by parts' rule...

Kind regards

$\chi$ $\sigma$
 
hah. thanks..
that was mildly embarrassing.

i didn't closely to see if he had done so. when he was talking in the lecture he mentioned that there was a 'trick' way to integrate this w/o integrating by parts or something along those lines.
 
nacho said:
hah. thanks..
that was mildly embarrassing.

i didn't closely to see if he had done so. when he was talking in the lecture he mentioned that there was a 'trick' way to integrate this w/o integrating by parts or something along those lines.

I would ask him again what it was he said. By-parts is certainly the standard way to integrate this, and it's not all that difficult, once you know how. I suppose you could set up tabular integration, but that's just a unified way of keeping track of by-parts. It wouldn't be worth it for only one application of by-parts.
 
The first step depends upon the fact that \frac{d(e^{-st})}{dt}= -s e^{-st} so that, dividing both sides by -s, e^{-st}= -\frac{1}{s}\frac{d(e^{-st})}{dt}.

Of course, since "s" is independent of the integration variable, t, we can take -\frac{1}{s} out of the integral.
 

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