Method of Variation of Parameters

In summary, the conversation discusses the need for two solutions in order to apply a specific method to solve a problem. The first solution is given, but the second one needs to be found in order to use the method. The conversation mentions the use of the characteristic equation and the possibility of using the Reduction of Order method to find the second solution.
  • #1
Augmented
5
0
Allright, I understand that we need two solutions to be able to apply the method like [tex]y_{1}[/tex] and [tex]y_{2}[/tex]

Problem gives 1 of them or let's you find only that 1 solution. But I can't apply the method since I don't have the other solution. The method I know is:

[tex]u_{1}'(x)y_{1}(x)+u_{2}'(x)y_{2}=0[/tex]
[tex]u_{1}'(x)y_{1}'(x)+u_{2}'(x)y_{2}'=g(x)[/tex]

solve for the [tex]u_{1}'(x)[/tex] and [tex]u_{2}'(x)[/tex] and do the integrals, solve the problem.

This is the problem I'm tackling with:

Find a value of [tex]p[/tex] such that [tex]e^{px}[/tex] is a solution of
[tex]xy''+(x-1)y'-y=2x^{2}e^{-x}[/tex]

well i can find out that p=-1 and its correct I'm pretty sure. How can I handle the rest of it as i mentioned above?
Thanks.
 
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  • #2
So first you need to do something else. Perhaps your textbook has this also: in a second-order homogeneous linear DE, given one solution to find the other one. As you note, you need to have both solutions of the homogeneous DE before you can apply the method of variation of parameters to get a solution of the inhomogeneous DE.
 
  • #3
g_edgar said:
So first you need to do something else. Perhaps your textbook has this also: in a second-order homogeneous linear DE, given one solution to find the other one. As you note, you need to have both solutions of the homogeneous DE before you can apply the method of variation of parameters to get a solution of the inhomogeneous DE.

Should it be writing down characteristic equation ?? I see no way out with the [tex]x[/tex] and [tex]x-1[/tex] that are coefficients to [tex]y''[/tex] and [tex]y'[/tex]. As I write it like this:

[tex]xr^{2}+(x-1)r-1=0[/tex]
umm, 2 unknowns, 1 equation ? Maybe with the known solution helps here? How?
 
  • #4
Allright, I think i found a clue: Reduction of Order method will let us find the other solution ? Please someone confirm it whether wrong or right. Thanks
 
  • #5
Augmented said:
Reduction of Order

right
 

1. What is the Method of Variation of Parameters?

The Method of Variation of Parameters is a mathematical technique used to find a particular solution to a non-homogeneous linear differential equation. It involves using a trial solution that includes undetermined coefficients, which are then determined by substituting the trial solution into the original equation.

2. When is the Method of Variation of Parameters used?

The Method of Variation of Parameters is used when the coefficients in a non-homogeneous linear differential equation are not constant and cannot be solved by other methods such as the Method of Undetermined Coefficients or the Method of Integrating Factors.

3. How does the Method of Variation of Parameters work?

The Method of Variation of Parameters works by assuming a trial solution in the form of y = u1y1 + u2y2, where u1 and u2 are undetermined coefficients and y1 and y2 are the two linearly independent solutions of the corresponding homogeneous equation. The undetermined coefficients are then determined by substituting this trial solution into the original equation and solving for u1 and u2.

4. What are the advantages of using the Method of Variation of Parameters?

The Method of Variation of Parameters allows for the solution of non-homogeneous linear differential equations with non-constant coefficients, which cannot be solved by other methods. It also provides a more general solution compared to the Method of Undetermined Coefficients, which only works for specific types of non-homogeneous equations.

5. Are there any limitations to the Method of Variation of Parameters?

One limitation of the Method of Variation of Parameters is that it can only be applied to linear differential equations. It also requires knowledge of the linearly independent solutions of the corresponding homogeneous equation, which may not always be easy to find. Additionally, the trial solution used may not always work for more complicated equations, requiring the use of other methods.

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