7  Invertible Matrices
Definition 6 If A is a square matrix of order m, and if there exists another square
matrix B of the same order m, such that AB = BA = I, then B is called the inverse
matrix of A and it is denoted by A– 1 In that case A is said to be invertible For example, let
A =
2
3
1
2






and B = 
2
3
1
2
−




−

be two matrices Now
AB =
2
3
2
3
1
2
1
2
−

 


 

−

 

=
4
3
6
6
1
0
I
2
2
3
4
0
1
−
− +




=
=




−
− +




Also
BA =
1
0
I
0
1

 =



