Integrating Factor: Solving (2y-6x)dx + (3x+4x2y-1)dy = 0

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In summary, the conversation is about solving a first order differential equation using an integrating factor. The equation is (2y-6x)dx + (3x+4x2y-1)dy = 0 and the attempt at a solution involves finding the integrating factor and using a substitution technique to make the equation separable. The conversation also mentions the option of solving for u and then y to find the integrating factor.
  • #1
annoymage
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Homework Statement



(2y-6x)dx + (3x+4x2y-1)dy = 0

Homework Equations





The Attempt at a Solution



(3xy+4x2)dy/dx = 6xy-2y2


i'm stuck, want to find the intergrating factor, it's xy2 when i reverse from the answer :D.. give me any hint please
 
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  • #2
or am i suppose to use special integrating factor??
 
  • #3
Are you sure there is an integrating factor? Maybe I'm just not seeing it. But you could also try the substitution v=y/x. That should make it separable.
 
  • #4
yey, i got it now, there's another technique which i don't really know the details..

But to find suitable intergrating factor,

its something like


e([tex]1/M[/tex])[([tex]N(x,y)/dx[/tex]) - ([tex]M(x,y)/dy[/tex])]

and is equal to xy2

and multiply both sides by the integrating factor, and will get Exact form of equation and solve it, hoho,

but maybe i need to try substituting v=y/x
 
  • #5
Every first order differential equation has an integrating factor- it just may be hard to find!

Are you required to find an integrating factor? this equation is "homogeneous". Write it as
[tex]\frac{dy}{dx}= \frac{6x- 2uy}{3x+ 4x^2y^{-1}}= \frac{6- 2\frac{y}{x}}{3+ 4\frac{x}{y}}[/tex]

Let u= y/x so that y= xu and dy/dx= u+ x du/dx and that will become a separable equation for u as a function of x. If you really want to find an integrating factor, I think that solving for u and then y and deriving the integrating factor from the solution is simplest.
 

FAQ: Integrating Factor: Solving (2y-6x)dx + (3x+4x2y-1)dy = 0

What is an integrating factor?

An integrating factor is a function that is multiplied to a differential equation in order to make it easier to solve. It is used to convert a non-exact equation into an exact one by making the coefficient of the differential term equal to 1.

How do you determine the integrating factor for a given differential equation?

The integrating factor for a given differential equation can be determined by finding the function that satisfies the integrating factor equation: (∂M/∂y) - (∂N/∂x) = N * (d/dx)u - M * (d/dy)u, where M and N are the coefficients of the differential terms in the equation and u is the integrating factor. Once this equation is solved, the integrating factor can be found by taking the exponential of the solution.

Why is an integrating factor useful in solving differential equations?

An integrating factor is useful because it can transform a non-exact differential equation into an exact one, making it easier to solve. It can also be used to solve differential equations that cannot be solved by other methods, such as separation of variables or substitution.

Can any differential equation be solved using an integrating factor?

No, not all differential equations can be solved using an integrating factor. It is only applicable to certain types of equations, such as first-order linear equations or certain types of second-order equations.

How do you use an integrating factor to solve a differential equation?

To solve a differential equation using an integrating factor, follow these steps:
1. Identify the coefficients of the differential terms in the equation.
2. Use the integrating factor equation to find the integrating factor.
3. Multiply both sides of the equation by the integrating factor.
4. Simplify the equation and integrate both sides.
5. Solve for the dependent variable, typically denoted by y.
6. Check the solution by substituting it back into the original equation.

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