Integrate x/(x^2-2x+5): Clarifying Steps

  • Thread starter Thread starter Azureflames
  • Start date Start date
  • Tags Tags
    Integral
Azureflames
Messages
3
Reaction score
0

Homework Statement



Hi, I'm trying to take the integral of x/(x^2-2x+5) dx but I'm not sure what to do.

Homework Equations





The Attempt at a Solution



I started by completeing the square in the denominator giving me the integral of x/((x-1)^2+4)) dx but I am not sure where to go from there. I have the correct answer for it but I need to understand the steps involved getting there.

EDIT: Okay, after spending a decent amount of time on this problem I finally look for some place to get help, and 5 minutes later I think I come up with a solution.

First, I set u = x^2 - 2x +5, du/2 - 2/2 = x. Substituted back in which gave me (1/2)integral( (du-2)/u ) which I then split into (1/2)integral(du/u) - (1/2)integral(2/u).

Taking the integral of the first part gave me (1/2)ln(x^2 - 2x +5). For the second half, I substitued the u values back into the equation which gave me: -(1/2)integral(2/(x^2 - 2x + 5). I completed the square in the denominator which gave me -integral( 1/((x-1)^2+4 ).

Integrating that part of the equation gives me -(1/2)arctan((x-1)/2).

So my final answer is (1/2)ln(x^2 - 2x +5) - (1/2)arctan((x-1)/2) + C. Can someone please confirm my steps? Sorry if my work is hard to follow. I wasn't sure how to make the proper symbols and my time is short :)
 
Last edited:
Physics news on Phys.org
That's right.
 
Hell, that seemed clever(or I suck)

I would've done partial fraction decomposition, and heaven knows NO ONE likes doing that
 
Prove $$\int\limits_0^{\sqrt2/4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx = \frac{\pi^2}{8}.$$ Let $$I = \int\limits_0^{\sqrt 2 / 4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx. \tag{1}$$ The representation integral of ##\arcsin## is $$\arcsin u = \int\limits_{0}^{1} \frac{\mathrm dt}{\sqrt{1-t^2}}, \qquad 0 \leqslant u \leqslant 1.$$ Plugging identity above into ##(1)## with ##u...

Similar threads

Replies
15
Views
2K
Replies
6
Views
2K
Replies
105
Views
4K
Replies
10
Views
2K
Replies
10
Views
2K
Replies
22
Views
3K
Replies
27
Views
3K
Replies
12
Views
2K
Back
Top