a) X1=the set of all two by two matrices of the form
(a 0; b a) where a and b belong to Z(mod 2)
b) X2=the set of all two by two matrices of the form
(a+b b; b a) where a and b belong to Z (mod 2)
c) X3=the set of all two by two matrices of the form
(a a+b; 0 b) where a and b belong to Z (mod 2)
Which, if any, are isomorphic to each other...give isomorphisms or explain why not....