Originally Posted by

**davefulton** Dear all,

I have a vector identity and am confused about the notation

$\displaystyle

\bf a\times (\bf b\times \bf c)=\bf b(\bf a\cdot \bf c)-\bf c(\bf a\cdot\bf b)

$

where $\displaystyle \bf a$, $\displaystyle \bf b$ and $\displaystyle \bf c$ are vectors and $\displaystyle \times$ and $\displaystyle \cdot$ are the cross and dot product respectively.

My question is what is the operation between $\displaystyle \bf b(a$?

It isn't the dot product. Is it the scalar product? Also is it commutative?

$\displaystyle

\bf b(\bf a\cdot \bf c)-\bf c(\bf a\cdot\bf b)=(\bf a\cdot \bf c)\bf b-(\bf a\cdot\bf b)\bf c

$