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Homework Help: Integrating factor

  1. Sep 25, 2005 #1
    Howdy, I've read this forum for some time, however this is my first post. I am attempting to solve this ODE. I am looking to find an integrating factor, then solve. I have attached the link to the problem set if my input here is ambiguous. Number 4d. Thank you kindly for any help you might lend.


    (2x^2)+y+((x^2)*y)-x)dy/dx=0

    My reasoning takes me as far as the integrating factor being exp(int( ? )dx)

    https://people.creighton.edu/%7Elwn70714/DE_Assignments/DE%20Assignment%202%20PDF.pdf [Broken]
     
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Sep 25, 2005 #2
    (2x^2)+y+((x^2)*y)-x)dy/dx=0

    (2x^2+y)dx + [(x^2)*y-x]dy=0

    Now you just need re-read your text-book about how to solve Pdx+Qdy=0, after checking some conditions on P&Q if such an equation has roots or none.
     
  4. Sep 25, 2005 #3

    saltydog

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    Or can approach it this way:

    [tex](2x^2+y)dx+(x^2y-x)dy=0[/tex]

    So, after a quick check for homogeneous, exact, and explicit calc. of an integrating factor via partials, we expand the differentials and attempt to group them together to form exact differentials:

    [tex]2x^2dx+ydx+x^2ydy-xdy=0[/tex]

    Well, the ydx-xdy can be grouped as:

    [tex]y^2\left(\frac{ydx-xdy}{y^2}\right)[/tex]

    This leaves us with:

    [tex]2x^2dx+x^2ydy+y^2 d\left(\frac{x}{y}\right)[/tex]

    Can you re-arrange this now to obtain exact differentials which can be integrated?
     
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