Diff Eq- Nonhomogeneous Equations

In summary, the conversation discusses finding a particular solution for the given equation y^''' + 4y^' = 3x-1 using the method of Undetermined Coefficients. The solution is y(x)=(3/8)x^2 - (1/4)x, found by multiplying the general solution by x and adding another term. The conversation also mentions another question about finding a particular solution for 4y^'' + 4y^' + y = 3xe^x, which also requires the method of Undetermined Coefficients.
  • #1
Totalderiv
70
1

Homework Statement


Find a particular solution of the given equation.
[tex] y^''' + 4y^' = 3x-1[/tex]

Homework Equations



[tex] r^3 + 4r = 0 [/tex]
[tex] r = 0, r = 2i, r = -2i[/tex]

The Attempt at a Solution


[tex]y(x) = Ax-B[/tex]
[tex]y^'(x) = A[/tex]
[tex]y^''(x) = 0[/tex]
[tex]y^'''(x) = 0[/tex]


The answer is:
[tex]y(x)=(3/8)x^2 - (1/4)x[/tex]
But I'm not sure how they came to this, please help!
 
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  • #2
r=0 gives a constant as a solution of the homogeneous equation. So instead of trying Ax+B you must multiply by x and try ##y_p=Ax^2+Bx##.
 
  • #3
Totalderiv said:
Thanks! I have another question though,

[tex] 4y^'' + 4y^' + y = 3xe^x [/tex]

How do I start this?

The same way you started the other one. You find the complementary solution and then use Undetermined Coefficients for the particular solution. Surely your text discusses the method of Undetermined Coefficients, doesn't it?
 

Related to Diff Eq- Nonhomogeneous Equations

1. What is a nonhomogeneous differential equation?

A nonhomogeneous differential equation is a type of differential equation where the right-hand side is not equal to zero. This means that there is an external influence or forcing function acting on the system, making it nonhomogeneous.

2. How do you solve a nonhomogeneous differential equation?

To solve a nonhomogeneous differential equation, you can use the method of undetermined coefficients or the variation of parameters method. These methods involve finding a particular solution that satisfies the nonhomogeneous part of the equation, combined with the general solution of the corresponding homogeneous equation.

3. What is the difference between a homogeneous and nonhomogeneous differential equation?

A homogeneous differential equation has a right-hand side equal to zero, meaning there is no external influence or forcing function. On the other hand, a nonhomogeneous differential equation has a non-zero right-hand side, indicating the presence of an external influence on the system.

4. Can a nonhomogeneous differential equation have a unique solution?

No, a nonhomogeneous differential equation can have multiple solutions depending on the initial conditions. However, with the addition of a particular solution, the equation can have a unique solution.

5. What are some real-life applications of nonhomogeneous differential equations?

Nonhomogeneous differential equations are used to model a wide range of physical phenomena, such as population growth, radioactive decay, and electrical circuits with external sources. They are also used in engineering fields to study systems with external influences, such as control systems and fluid dynamics.

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