If the sets A and B are defined as
A=x,y:y=1x,0≠x∈R
B=(x,y):y=-x,x∈R, then
A∩B=A
A∩B=B
A∩B=∅
None of these
solving, we get -x=1x ⇒x2=-1 which is not possible in real system ⇒A∩B=∅