Integrals: Why Use Arctan Formula?

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Discussion Overview

The discussion revolves around the integral \(\int\frac{dx}{\sqrt{x}(x + 1)}\) and the application of the arctan formula in its evaluation. Participants explore the use of u-substitution and the steps involved in rewriting the integral, while also addressing potential errors in the differentiation process.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant questions the necessity of using the arctan formula for the given integral, suggesting it is typically used for integrals of the form \(\int\frac{du}{a^2 + u^2}\).
  • Another participant proposes using u-substitution with \(u = \sqrt{x}\) and provides steps leading to \(\int \frac{du}{u^2 + 1}\), indicating a path to the solution.
  • A participant expresses confusion about the correctness of the proposed solution, prompting further clarification.
  • There is a correction regarding the differentiation of \(x = u^2\), with one participant noting that a factor of 2 was missed in the earlier steps.
  • Another participant confirms the differentiation process but highlights that it was not accounted for in the previous post, indicating a need for careful attention to detail.
  • A participant acknowledges the oversight and attributes it to frustration with their computer, suggesting that errors can occur in the process of solving integrals.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the application of the arctan formula for the integral in question. There are competing views regarding the correctness of the proposed solution and the differentiation steps involved.

Contextual Notes

There are unresolved issues regarding the handling of constants during differentiation and the implications of those errors on the integral's evaluation. The discussion reflects varying levels of clarity on the substitution process and its execution.

RadiationX
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i don't see why the following integral:[tex]\int\frac{dx}{\sqrt{x}(x + 1)}[/tex] uses the arctan formula. i know how to solve integrals. i just don't see why or how you can rewrite it using the arctan formula. Isn't the arctan formula used for integrals of the form: [tex]\int\frac{du}{a^2 + u^2}=\frac{1}{a}arctan\frac{u}{a}[/tex]
 
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[tex]\int \frac{dx}{\sqrt{x}(x+1)}[/tex]
you have to use u-substitution.
so, you have:
[tex]u = \sqrt{x}~~~du=\frac{1}{2 \sqrt{x}[/tex]
now, here's where it gets tricky:
[tex]x=u^2[/tex]
now, you can substitute back in.
[tex]\int \frac{du}{u^2+1}[/tex]
now, just integrate and plug u back in, and you are done.

*edit* it isn't let me post du...well, i can't see it from my comp, but du = 1/2sqrt(x)dx
 
Last edited:
thanks i see now.
 
i just read your edit. is your solution incorrect?
 
He missed the 2 when differentiating [itex]x=u^{2}[/itex].

Daniel.
 
[tex]u = \sqrt{x}[/tex]
[tex]du = \frac{1}{2}x^{-\frac{1}{2}}dx[/tex]

? What is wrong with that?
 
Nothing,just that u didn't take it into account in the post i was referring to.

Daniel.
 
hehe, yea i left out the 2...so its half the integral when you work it out. this computer at work was frustrating me, so i forgot it. (my excuse :smile: )
 

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