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 engininja March 26th, 2011 01:24 AM

Another Inexact ODE

Okay so I have another working check
(2x+y^2)dx+ 4xy dy = 0
its not exact and we get an integrating factor of 1/sqrt(x)
u = integrate N(x,y) dy + g(x)
=2*sqrt(x)*y^2 + g(x)

also partial derivative du/dx = M(x,y) = (2x+y^2)/sqrt(x) and also = y^2/sqrt(x)+g'(x)
so g'(x) = 2x
and g(x) = 2x^2/2 = x^2
so implicit solution is 2*sqrt(x)*y^2+x^2
Can someone please confirm or deny.

 MarkFL March 26th, 2011 05:40 AM

Re: Another Inexact ODE

You have:

You are right, this is not exact, so we consider:

Since this is a function of just x, we obtain an integrating factor by:

This gives the exact equation:

thus:

Integrating with respect to x, we get:

To determine g(y), we take the partial derivative with respect to y and substitute N for :

thus the solution is given implicitly by:

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