contestada

Which of the following matrix calculations are well defined (the sizes match)? If the computation makes sense, perform it.
( (a) ) ( AA )
( (b) ) ( BB )
( (c) ) ( CC )
( (d) ) ( DD )
a) ( (b) ) ( BB )
b) ( (a) ) ( AA )
c) ( (c) ) ( CC )
d) ( (d) ) ( DD )