Solution (source code)

= Solution

The <vector triple product identity> is
$$
\boxed{a\times(b\times c)=b(a\cdot c)-c(a\cdot b).}
$$
Thus the expression lies in the <linear span> of $b$ and $c$, with respective <scalar> coefficients $a\cdot c$ and $-a\cdot b$. The order and the minus sign matter because the <cross product> is not an <associative operation>.