This is a 2 × 2  matrix in which each
entry is the sum of the products across some row of C with the corresponding entries
down some column of D These four computations are
Thus 
13
2
CD
17
13
−


= 

−


Example 12 Find AB, if 
6
9
2
6
0
A
and B
2
3
7
9
8




=
=







 Solution The matrix A has 2 columns which is equal to the number of rows of B Hence AB is defined