$A = \begin{pmatrix} 1 & -2 & -1 \\ 0 & 4 & -1 \\ -3 & 2 & 1 \end{pmatrix}, B = \begin{pmatrix} -2 \\ -5 \\ -7 \end{pmatrix}, C=[9,8,7]$Order of A is $3 \times 3$Order of B is $3 \times 1$Order of C is $1 \times 3$Product of two matrices A and B is defined if the number of columns in matrix A is equal to number of rows in matrix B.No. of column of matrix A = no. of rows of matrix B∴ A B is definedNo. of column of matrix A = 3∴ no. of row of matrix C = 1∴ A C is not defined.No. of column of matrix B is not equal to no. of rows matrix A.So, BA is not defined.No. of column of A is not equal to no. of row of C∴ A C is not defined