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In chapter 20 of "Foundations of Electromagnetic theory" by Reitz,Milford and Christy,there is calculation which seems to make use of:[itex] \vec{\nabla}\times\dot{\vec{p}}=\Large{\frac{\vec{r}}{r}\times\frac{ \partial \dot{\vec{p}}}{\partial r}} [/itex] where [itex] \dot{\vec{p}}=\large{\frac{d}{d \tau}} \int_V \vec{r}'\rho(\vec{r}',t-\frac{r}{c})dv' \ (\tau=t-\frac{r}{c})[/itex].But I can't prove it and worse is that it seems to be inconsistent with the formula for curl in spherical coordinates.

There is also another identity mentioned in the problems of chapter 1 which seems as strange:

[itex]\vec{\nabla}\cdot\vec{F}(r)=\large{\frac{\vec{r}}{r}\cdot\frac{d\vec{F}}{dr}} [/itex]

Is there any suggestion?

Thanks

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# Vector differential identities

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