This is part of a bigger derivation of Green's function. The book just jump to the ending and I cannot understand how to do this. I need someone to give me guidence how to proof this:(adsbygoogle = window.adsbygoogle || []).push({});

[tex] \frac{x}{r} \frac{\partial u}{\partial x} + \frac{y}{r} \frac{\partial u}{\partial y} +\frac{z}{r} \frac{\partial u}{\partial z} \;=\; \frac{\partial u}{\partial r} [/tex]

Where

[tex] r=\sqrt{x^2+y^2+z^2}[/tex]

This is not a homework problem.

Thanks

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# Can anyone help me proofing this? This is not homework.

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