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Integrating factor

by roryhand
Tags: factor, integrating
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roryhand
#1
Sep25-05, 12:59 AM
P: 2
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/%7Elwn7...%202%20PDF.pdf
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Emieno
#2
Sep25-05, 01:57 AM
P: 109
(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.
saltydog
#3
Sep25-05, 03:10 AM
Sci Advisor
HW Helper
P: 1,593
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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