Assistance with Third Order Differential Equation

In summary, the speaker is asking for help with solving the equation y''' + 8y = xsin(2x) and has proposed a possible solution of the form yp=Axsin(2x)+Bxcos(2x)+Csin(2x)+Dcos(2x). They have also provided their attempt at solving the homogeneous DE, which does not contain any terms like the NH term. They are asking for feedback on their proposed solution.
  • #1
kelvin2013
2
0

Homework Statement


Hi,

Just wondering if anyone knows how to solve the following as I am not sure where to start at all:

y''' + 8y = xsin(2x)

Any help would be great.


Homework Equations






The Attempt at a Solution



I'm thinking solving the homogeneous DE y'''+8y = 0 and then as far as I can see a possible solution maybe of the form yp=Axsin(2x)+Bxcos(2x)+Csin(2x)+Dcos(2x) ?
 
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  • #2
kelvin2013 said:

Homework Statement


Hi,

Just wondering if anyone knows how to solve the following as I am not sure where to start at all:

y''' + 8y = xsin(2x)

Any help would be great.


Homework Equations






The Attempt at a Solution



I'm thinking solving the homogeneous DE y'''+8y = 0 and then as far as I can see a possible solution maybe of the form yp=Axsin(2x)+Bxcos(2x)+Csin(2x)+Dcos(2x) ?

What do you get for ##y_c## when you solve the homogeneous DE? You need to know that before you can predict the form of the NH equation.
 
  • #3
Hi,

thanks for the reply - I get:

yp=c1e-2x+c2e(1+i√3)x+c3e(1-i√3)x

?
 
  • #4
kelvin2013 said:
Hi,

thanks for the reply - I get:

yp=c1e-2x+c2e(1+i√3)x+c3e(1-i√3)x

?

OK. So far so good. It would be nicer to use sines and cosines instead of the complex exponentials. Anyway, your complementary solution doesn't contain any terms like the NH term. So what happens when you try your proposed ##y_p##?
 

Related to Assistance with Third Order Differential Equation

1. What is a third order differential equation?

A third order differential equation is a mathematical equation that involves a function and its first, second, and third derivatives. It can be written in the form of y''' = f(x, y', y'', y''').

2. Why do we need assistance with third order differential equations?

Third order differential equations can be complex and difficult to solve, especially when they involve real-life problems. Assistance with these equations can help to simplify and solve them more efficiently.

3. What are some common methods used to solve third order differential equations?

The most common methods used to solve third order differential equations are substitution, variation of parameters, and Laplace transforms. These methods involve manipulating the equation to reduce it to a simpler form that can be solved more easily.

4. Can third order differential equations be solved analytically?

It depends on the specific equation and the initial conditions given. Some third order differential equations can be solved analytically, while others may require numerical methods or approximation techniques to find a solution.

5. How are third order differential equations used in scientific applications?

Third order differential equations are used in many scientific fields, including physics, engineering, and biology. They can be used to model and solve real-world problems involving motion, growth, and other dynamic processes.

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