TDSM 8.1
From The Data Science Design Manual Wikia
a) [math] A = \begin{bmatrix} 1 & 2\\ 2 & 3 \end{bmatrix} [/math], [math] B = \begin{bmatrix} 1 & 0\\ 0 & 1 \end{bmatrix} [/math]
[math] \Rightarrow AB = BA = \begin{bmatrix} -2 & 1\\ -5 & 2 \end{bmatrix} [/math]
b) [math] A = \begin{bmatrix} 0 & 1\\ 0 & 0 \end{bmatrix} [/math], [math] B = \begin{bmatrix} 1 & 0\\ 0 & 0 \end{bmatrix} [/math]
[math] \Rightarrow AB = \begin{bmatrix} 0 & 0\\ 0 & 0 \end{bmatrix}, BA = \begin{bmatrix} 0 & 1\\ 0 & 0 \end{bmatrix} [/math]
