## College Algebra 7th Edition

$\left[\begin{array}{lll} 4 & \fbox{$9$} & -7\\ 7 & -7 & \fbox{$0$}\\ \fbox{$4$} & -5 & -5 \end{array}\right]$
$AB=C$ $c_{ij}=$the inner product of (row $i$ of A) times (column $j$ of B) ---- The missing entry in $c_{12}$ row 1, column 2, is the inner product of (row 1 of A) times (column 2 of B) $c_{12}=3(3)+1(-2)+2(1)=9$ $c_{23}=-1(-2)+2(-1)+0(0)=0$ $c_{31}=1(-1)+3(3)-2(2)=4$