Let $\vec{a} ,\vec{b},\vec{c}$ linear Independent vectors that form and ordered basis B. And consider this basis non orthogonal and $\vec{r} = x \vec{a} +y\vec{b}+z\vec{c}$. This vector space is euclidian and Real. Prove that:
$\displaystyle x = \frac{\vec{r} \cdot \vec{b}\times\vec{c}}{\vec{a} \cdot \vec{b}\times\vec{c}}$
