Method of Undetermined Coefficients

In summary, when finding the general solution for the equation y(4)-4y2=t2+et, it is important to first determine the complementary solution. Then, when assuming a particular solution, it is necessary to start with a 4th degree term in order to avoid having the same term as the complementary solution. This can be achieved by multiplying the particular solution by t if needed.
  • #1
polarbears
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Homework Statement


y(4)-4y2=t2+et
Determine the general solution

Homework Equations





The Attempt at a Solution



So I worked it all out and got the correct answer. My question is that when we make the onsat that a particular solution will be in the form Y=At4+...how do we know it starts with a 4th degree? It doesn't make sense to me since the right hand side is a 2nd degree
 
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  • #2
You get better at guessing particular solutions.

First you have to get the complementary solution. Once you have that assume that the y is something like At2 + Bet. You're fine up until now as long as your complementary solution doesn't have the same term in it. Otherwise you will have to multiply your particular solution by t.

You complementary solution will be of the form Atet + Bet. Since the particular solution has the same term Bet, you multiply once by t to get Btet, but that's the same form as Atet. So you have to multiply by t again. Resulting in the 4th degree.
 

FAQ: Method of Undetermined Coefficients

1. What is the Method of Undetermined Coefficients?

The Method of Undetermined Coefficients is a technique used in mathematics and science to solve differential equations with non-homogeneous terms. It involves finding a particular solution to the equation by assuming a form for the solution and then solving for the coefficients.

2. When is the Method of Undetermined Coefficients used?

The Method of Undetermined Coefficients is used when solving non-homogeneous linear differential equations, where the non-homogeneous term is a polynomial, exponential, trigonometric, or a combination of these functions. It cannot be used for non-linear equations or equations with non-constant coefficients.

3. How does the Method of Undetermined Coefficients work?

The method works by assuming a particular form for the solution, which is usually the same as the non-homogeneous term. The unknown coefficients in the assumed form are then determined by plugging the solution into the original equation and solving for the coefficients using algebraic techniques.

4. What are the advantages of using the Method of Undetermined Coefficients?

The Method of Undetermined Coefficients is a relatively simple and efficient method for solving non-homogeneous linear differential equations. It also provides a general solution, meaning that it can be used for a wide range of equations with different non-homogeneous terms.

5. Are there any limitations to the Method of Undetermined Coefficients?

One limitation of the method is that it only works for non-homogeneous linear differential equations with specific types of non-homogeneous terms. It also relies on guessing the form of the solution, so it may not always provide an accurate solution. In some cases, it may be necessary to use other methods, such as the Variation of Parameters method, to find a particular solution.

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