Integrate sqrt(u-2): Trig or Straight Away?

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Discussion Overview

The discussion revolves around the integration of the function sqrt(u-2) following a u-substitution. Participants explore whether to integrate directly or to apply trigonometric substitution, examining the implications of each approach.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether they can integrate sqrt(u-2) directly or if trigonometric substitution is necessary.
  • Another participant advises against using trigonometric substitution, suggesting that it complicates the process unnecessarily.
  • Several participants propose using a substitution v = u - 2 to simplify the integral, indicating that this approach leads to an easier integration.
  • A participant emphasizes that substitutions are not mandatory and should only be used to simplify the problem, noting that integrating directly is permissible if the participant feels confident in the answer.
  • It is mentioned that trigonometric substitution is generally useful for integrals involving sums or differences of squares, but not required in this case.

Areas of Agreement / Disagreement

Participants generally agree that trigonometric substitution is not necessary for this integral, but there is some uncertainty regarding the appropriateness of integrating directly versus making further substitutions.

Contextual Notes

Some participants express uncertainty about the necessity of further substitutions after an initial u-substitution, highlighting the subjective nature of the integration process.

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I was doing a question using u substitution and at one point,I got sqrt(u-2). How do I integrate it further?

Can I integrate is straight away with sqrt(u-2)(2/3) as answer or do I have to use trigonometric substitution? How to do if it's trigonometric?
 
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Don't bother about the trig substitution. It will hiss at you, just as a nasty and venomous serpent would do.

And if you feel uncertain about integrating straight away, just substitute with the new variable s=u-2, and see where that leads you.
 
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So,I don't have to use trigonometric substitution?
 
Why tread on a rattle snake?
Much easier to substitute v=u-2
 
Can I just integrate straight away? I mean I already u-substitution already do I need to do another substitution?
 
You never "need" to do any type of substitution. Substitutions are made in order to simplify the problem, but if the problem is simple enough (i.e, you what the answer will be), then there is not much point in further simplification, is there.

However, you expressed an uncertainty as to whether it was "allowed" to integrate straight away. (Everything is allowed to do in maths, provided it is correct. :smile:)

In order to alleviate that uncertainty, I pointed out to you that you CAN make the u-2 substition, if that makes you feel safer in doing the right thing.
 
To elaborate on what arildno said, if you make the substitution v = u - 2, then dv = du, so the integral changes like so:
$$ \int \sqrt{u - 2}du = \int \sqrt{v}dv$$

The latter integral is pretty easy. A trig substitution is not needed here, but is very useful if the quantity in the radical is a sum or difference of squares.
 

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