`BA=(4\ \ -1\ \ \ 5)((-2,1,7),(3,-1,0),(0,2,-1))`

`=( -8+(-3)+0\ \ \ 4+1+10\ \ \ 28+0+(-5))`

`=(-11\ \ 15\ \ 23)`

AB is not possible. (3 × 3) × (1 × 3).

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