- #1

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In the book of astrodynamics I'm currently reading, I came across this expansion:

[tex](\vec{r}\times\vec{v})\times\vec{r}=[\vec{v}(\vec{r}\cdot\vec{r})-\vec{r}(\vec{r}\cdot\vec{v})][/tex]

Can anyone explain how this result is arrived at? If any physical significance is needed, r is a position vector and v its derivative with respect to time, the velocity vector.