Solve by using variation of parameters

In summary, the given equation involving x, y, and their derivatives can be transformed into a constant coefficient problem by substituting t=ln(x). This can simplify the problem and make it easier to solve.
  • #1
SOS2012
4
0
x²y"(x)-3xy'(x)+3y(x)=2(x^4)(e^x)

=>y"(x)-(3/x)y'(x)+(3/x²)y(x)=2x²e^x

i don't know how to approach this problem because the coefficients are not constant and i am used to being given y1 and y2

HELP!
 
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  • #2
This is an "Euler type" or "equi-potential" equation. The substitution t= ln(x) will change it to a "constant coefficients" problem in the variable t.

[tex]\frac{dy}{dx}= \frac{dy}{dt}\frac{dt}{dx}= \frac{1}{x}\frac{dy}{dt}[/tex]
and, differentiating again,
[tex]\frac{d^2y}{dx^2}= \frac{d}{dx}\left(\frac{dy}{dx}\right)[/tex][tex]= \frac{d}{dx}\left(\frac{1}{x}\frac{dy}{dt}\right)= -\frac{1}{x^2}\frac{dy}{dt}+ \frac{1}{x^2}\frac{d^2y}{dt^2}[/tex]
 
  • #3
HallsofIvy said:
This is an "Euler type" or "equi-potential" equation. The substitution t= ln(x) will change it to a "constant coefficients" problem in the variable t.

[tex]\frac{dy}{dx}= \frac{dy}{dt}\frac{dt}{dx}= \frac{1}{x}\frac{dy}{dt}[/tex]
and, differentiating again,
[tex]\frac{d^2y}{dx^2}= \frac{d}{dx}\left(\frac{dy}{dx}\right)[/tex][tex]= \frac{d}{dx}\left(\frac{1}{x}\frac{dy}{dt}\right)= -\frac{1}{x^2}\frac{dy}{dt}+ \frac{1}{x^2}\frac{d^2y}{dt^2}[/tex]
thank you very much. i appreciate the help
 

1. What is the variation of parameters method?

The variation of parameters method is a technique used to solve a non-homogeneous linear differential equation. It involves finding a particular solution by assuming a general form and then solving for the coefficients using the original equation.

2. When is the variation of parameters method used?

The variation of parameters method is typically used when the non-homogeneous term in a linear differential equation is a polynomial, exponential, or trigonometric function. It is also used when the coefficients of the equation are not constant.

3. How is the variation of parameters method applied?

To apply the variation of parameters method, the following steps are typically followed:

  • Find the complementary function by solving the associated homogeneous equation.
  • Assume a particular solution in the form of a linear combination of the fundamental solutions of the homogeneous equation.
  • Substitute the particular solution into the original equation and solve for the coefficients.
  • Add the complementary function and the particular solution to get the general solution to the original equation.

4. What are the advantages of using the variation of parameters method?

The variation of parameters method allows for the solution of non-homogeneous linear differential equations with non-constant coefficients. It also provides a more general solution compared to other methods, which only provide specific solutions for particular types of equations.

5. Are there any limitations to the variation of parameters method?

One limitation of the variation of parameters method is that it can be quite complex and time-consuming to apply, especially for higher-order differential equations. It also may not work for all types of non-homogeneous terms, such as those that are not continuous or differentiable.

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