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Second-Order Nonhomogeneous DE

  • Thread starter ohgeecsea
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  • #1
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The Equation:

x^2 (d^2y/dx^2) + 3x (dy/dx) - 3y = x

The boundary conditions:

y(x=1) = 0
y(x=2) = 1

It's been awhile since I took diffeq, but my research has led me to believe that this is not a Cauchy-Euler Equation since it is not equal to 0, it cannot be separated for separation of variables, it cannot be solved using reduction of order because I was not given one solution, and I cannot solve using Laplace transforms because I was not given initial values, just boundary conditions.

I considered dividing by x^2 or x, but that leaves me either with a constant (still not 0) or a term that has both x and y in it, which I wouldn't know how to solve either.

I just re-imaged my laptop so I do not currently have MATLAB, but if I did I would not be quite sure how to go about it. WolphramAlpha didn't read the equation correctly. I have flipped through a friend's diffeq book and that yielded nothing helpful.

It seems likely that this has a simple solution because this homework was intended as a review of diffeq, so I'm sure a large part of the problem is that I'm rusty and have overlooked something. Help?
 

Answers and Replies

  • #2
fzero
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  • #3
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This is an inhomogeneous Cauchy-Euler ODE !

As always with linear ODEs you can find the homogeneous solution to the ODE and add the particular solution to get the full solution.

Technically you can not use the Undetermined Coefficients method, it can only be used with constant coefficient ODEs.

But you can still guess the particular solution (guess Ax).

The rigorous way to solve it is to use substitution: x = exp(z)

http://en.wikipedia.org/wiki/Cauchy–Euler_equation
 
  • #4
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