Mnn is a space of all m x n matrices Symmetric matrix Snn are in M and is a subset of all symmetric matrices, exchanges rows and columns such as A=AT (A,B) are in Symmetric matrices such as (aij=aji or bij=bji) an example of this is A+B==aij+bij, therefore (A+B)T = (aji+bji)=(BT)+(AT) hope this helps.