So, the question is: find the gradient of f=ln(r), where r=sqrt(x^2+y^2+z^2)^(1/2).(adsbygoogle = window.adsbygoogle || []).push({});

For the partial with respect to x, I use the chain rule: df/dr*dr/dx.

df/dr=1/r

dr/dx=(1/2)*(2x)=x

Which would give df/dx = x/r.

But the book gets x/r^2

Where does the extra 1/r come from?

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# Homework Help: Simple derivative question

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