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Niles

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## Homework Statement

Please take a look at the example at the bottom (at eq. 18:18, at page 619):

http://books.google.dk/books?id=9p6...g=iAUGf-f9d5uHRwwYZnpFpA8HJDA&hl=da#PPA619,M1

Q1: In case (ii), why do they add g(x^2+y^2)?

Q2: Why do they not add it in case (i)?

Q3: In case (ii), if I chose f(p) = p + 1 instead of f(p) = 2p, then the solution would be u(x,y) = 1+ x^2 +y^2 + g(x^2 + y^2), right?

I hope you can help me; I find this really hard to understand, and I've spent hours trying to find out, but I find that the book is poorly written. They don't emphasize the important things at all, and the reader is left behind with so many questions.

Thanks in advance.

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