\[\mathbf a\times\mathbf b=|\mathbf a||\mathbf b|\sin\theta\,\widehat{\mathbf n},\qquad \widehat{\mathbf n}\perp\mathbf a,\mathbf b\]
Right-hand orientation
\[\mathbf a\times\mathbf b=\begin{vmatrix}\mathbf i&\mathbf j&\mathbf k\\a_1&a_2&a_3\\b_1&b_2&b_3\end{vmatrix},\qquad \mathbf b\times\mathbf a=-(\mathbf a\times\mathbf b).\]
For nonzero vectors, \(\mathbf a\times\mathbf b=\mathbf0\) exactly when they are parallel. The product is distributive but not commutative or associative; cancellation is not generally valid.
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