Q f(x, y)=|x+y|g(x, y)=|x|+|y|h(x, y)=|x-y|l(x, y)=|x|-|y|If f(x, y)=g(x, y) and h(x, y)=l(x, y), and xy not equal to 0, then which of the following is necessarily true?

1) x+y>0
2) xy>0
3) x-y>0
4) x-y<0
5) None of these