Solving Linear ODEs: Question & Answer

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SUMMARY

The discussion focuses on solving a linear ordinary differential equation (ODE) where the user questions the validity of assuming a particular solution, η(x), without it being explicitly stated. The user initially attempts to substitute y = η + 1/ψ, leading to a complex equation involving p(x) and q(x). A critical correction is made regarding the differentiation notation, clarifying that dx/dψ should be expressed as -(1/ψ²)dψ/dx, which resolves the confusion in the equation's manipulation.

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physicsjock
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Hey,

I have been trying to work out how to solve this example question I found in a recommended text,

http://img715.imageshack.us/img715/5052/asdavm.jpg

Everywhere I've been reading starts with since y=eta(x) is a particular solution then y=eta(x) + u is a general solution, but the question doesn't state eta(x) as a particular solution, is that a problem?

Anyway in this question is the way to go simply subbing in y = eta + 1/si then noting that all the lone eta components cancel since they are a solution themselves.

But when I do that,

I end up with something like

\frac{dx}{d\Psi }=\left[ p(x)+2q(x)\eta (x) \right]\Psi (x)+\frac{q(x)}{{{\Psi }^{2}}(x)}

and I can't rearrange it to form the equation which si solves,

any idea on what I've done wrong?
 
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hey physicsjock! :smile:

where did that dx/dψ come from? :confused:

it should be -(1/ψ2)dψ/dx :wink:

(and then you'll be able to multiply throughout by ψ2)
 
ahah what a silly mistake I made!

Thanks heaps!
 

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