(A= left( begin array lll 1 & -2 & 3 end array right) ), (X= left( begin array lll x & y & z end array right), B= left( begin array rrr 1 & -2 & 3 1 & 5 & 0 4 & -2 & 1 end array right) ) (C= left( begin array ccc (m+n)^ 2 & l^ 2 & l^ 2 ~m^ 2 & (n+l)^ 2 & ~m^ 2 n^ 2 & n^ 2 & (l+m)^ 2 end array right) )