if (a,b) is an ordered pair for x-y=5, is (b,a) also a solution?
The answer is no. Because solution (a,b) means x=a, y=b.and we have a-b=5. And (b,a) would mean x=b and y=a but then x-y=b-a=-(a-b)=-5≠5. So the pair (b,a) is not a solution.