Finding Solutions to 4th Order Differential Equations

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Homework Help Overview

The discussion revolves around solving a fourth-order differential equation of the form xy^(4) + 6y'" = 0. Participants are exploring methods and approaches to find a solution, with varying levels of understanding regarding the appropriate techniques for such equations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants question the original poster's use of the auxiliary equation, suggesting it may not be suitable for a fourth-order equation. There are discussions about trying specific forms of solutions, such as y=x^n, and the implications of variable coefficients on the methods used. Some participants propose transforming the equation to a simpler form or using substitutions to facilitate solving.

Discussion Status

The discussion is active, with several participants offering insights and alternative approaches. There is a recognition of the complexity of the problem, and while no consensus has been reached, various methods are being explored, indicating a productive exchange of ideas.

Contextual Notes

Some participants express frustration with the clarity of their textbooks and seek additional resources for better understanding. The original poster is looking for foundational guidance to navigate the problem effectively.

Mathgician
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Homework Statement


solve the given differential equation:

xy^(4) + 6y'" = 0

Homework Equations



No idea, I need something to get me started

The Attempt at a Solution



auxiliary equation:

m^4 + 6m^3 = 0

m^3(m+6)=0
3 roots with m = 0 and the other root is m = -6

so I got y = C1 + C2lnx + C3(lnx)^2 + C4x^-6

but, it is not the solution. Your help is greatly appreciated. Thank You.
 
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I don't quite know what you're doing here. The method you are using here seems to be the one that you use for a second order equation, however this is an equation of 4th order.

Take a look at the equation and try and spot a solution. In particular, you have a fourth derivative multiplied by x, and a third order derivative. Now, you know a function whose fourth derivative multiplied by x is equal to its third derivative (modulo constants). The function is xn. So, try the general solution y=xn. Plugging this into the ODE will give you a condition on n, which will enable you to obtain the particular solution.
 
Your auxiliary equation is wrong. You appear to have used the auxiliary equation for a "constant coefficients" equation when you have a variable coefficient- and then used the "Euler type" solution.

One way to handle this is to multiply then entire equation by x3 so that you get x4y(iv)+ 6x3y'''= 0, an "Euler-type" or "equipotential" equation. If you let y= xr you will get the correct auxilliary equation for this d.e.

Much simpler is to let u= y'''. Now the equation is xu'+ 6u= 0, a simple, separable first order differential equation. After you have solved that, let y'''= u= your solution and integrate three more times.
 
so the auxiliary method only works for 2nd order? Can you guys give me little more insight or any websites that would explain it to me further because my books was very vague in explain my problem or there were no example of such problem in the book. I hate my textbook. Thank you for your insights guys :shy:
 
can you give me hint on how to solve an equation that involves a particular solution? Thank you:biggrin:
 

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