例题 1.2

已知 $\mathbf{A}=(1,4,3),\mathbf{B}=\left(\begin{array}{l}2\\ 3\\ 1\end{array}\right)$, 则

$$AB=(1,4,3)\left(\begin{array}{l}2\\ 3\\ 1\end{array}\right)=17$$

但是

$$\mathbf{B}\mathbf{A}=\left(\begin{array}{l}2\\ 3\\ 1\end{array}\right)(1,4,3)=\left(\begin{array}{ccc}2& 8& 6\\ 3& 12& 9\\ 1& 4& 3\end{array}\right).$$