Find all 2 x 2 matrices A that have the property that for any 2 x 2 matrix B, \[\mathbf{A} \mathbf{B} = \mathbf{B} \mathbf{A}.\]
Let A = [ 1 0 ] Let B = [ a b ]
[ 0 1 ] [ c d ]
AB = [ a b]
[ c d ]
BA = [ a b ]
+68 
