where the hell does this 2 come from

[silver wing]

I can't find where this 2 comes from spent too long on it 😦 plz halp

Is it from chain rule with dfdr to f prime?

[small current]

These do not agree, please check

Also this doesn't make sense

[silver wing]

Yeah I know that last wasn't right

Let me check first part

Yeah it should just be 1/r

Still where is the 2 @small current

[silver wing]

Hello?

[small current]

\begin{align*}
r^2 &= x^2+y^2+z^2\
2r\frac{\partial r}{\partial x}&=2x\
\frac{\partial r}{\partial x}&=\frac{x}{r}\
\frac{\partial^2r}{\partial x^2}&=\frac{\partial}{\partial x}\left(\frac{x}{r}\right)\
&=\frac{r-x\frac{\partial r}{\partial x}}{r^2}\
&=\frac{r^2-x^2}{r^3}
\end{align*}

[faint fiber]

ℝafain

[silver wing]

Oh lol

[small current]

Sum over x, y and z and you get 3r^2 - r^2 in the numerator

[silver wing]

Thank you

I forgot r depends on x

[stable hill]

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