Question

If A×B = {{p,q} , { p , r }, { m , q }, {m , r }, { } } find A and B

Answer 1

Given A×B = {{p,q} , { p , r }, { m , q }, {m , r }, { } }
or A×B = {{p,q} , { p , r }, { m , q }, {m , r }}

A is the set of all first elements i.e
A = {p, m}   ----------(Since first element contains only p and m) and 
B is the set of all second elements.
B = {q, r} -------------(Since second element contains only q and r)