# A non-exact nonlinear first ODE to solve

Nipuna Weerasekara

## Homework Statement

Solve the following equation.

## Homework Equations

( 3x2y4 + 2xy ) dx + ( 2x3y3 - x2 ) dy = 0

## The Attempt at a Solution

M = ( 3xy4 + 2xy )
N = ( 2x3y3 - x2 )

∂M/∂y = 12x2y3 + 2x
∂N/∂x = 6x2y3 - 2x

Then this equation looks like that the integrating factor is (xM-yN).
IF = x3y4 + 3x2y

then the new equation would be:

(3xy^3+2)/(x^2y^3+3x)dx + (2xy^3-1)/(xy^4+3y)dy = 0

but then if we find that this new equation is exact or not, it proves that this is not exact.
If so what should I do?

Note:
x3y2 + x2/y = c

Mentor

## Homework Statement

Solve the following equation.

## Homework Equations

( 3x2y4 + 2xy ) dx + ( 2x3y3 - x2 ) dy = 0

## The Attempt at a Solution

M = ( 3xy4 + 2xy )
The above should be ##M = 3x^2y^4 + 2xy##
Nipuna Weerasekara said:
N = ( 2x3y3 - x2 )

∂M/∂y = 12x2y3 + 2x
∂N/∂x = 6x2y3 - 2x
You have a mistake above.
If ##M = 3x^2y^4 + 2xy## then ##M_y = 12x^2y^3 + 2x##
Since My ≠ Nx, that's enough to show that the equation is not exact.

Nipuna Weerasekara said:
Then this equation looks like that the integrating factor is (xM-yN).
IF = x3y4 + 3x2y
I taught diff. equations a number of times, but this isn't a trick that I remember. Where does xM - yN come from?
Nipuna Weerasekara said:
then the new equation would be:

(3xy^3+2)/(x^2y^3+3x)dx + (2xy^3-1)/(xy^4+3y)dy = 0
I'm not following this at all. If you can find an integrating factor, you multiply both sides of the original diff. equation by it. If it really is an integrating factor, then the new equation will be exact, and you can get the solution.
Nipuna Weerasekara said:
but then if we find that this new equation is exact or not, it proves that this is not exact.
If so what should I do?

Note:
x3y2 + x2/y = c