Mathematics for IGCSE & O level - Sets (Section 3 - No. 40)

If P and Q are disjoint sets, then:

P ∩ Q = P

P ∩ Q = Q

P ∩ Q = Ø

P ∪ Q = Ø

Disjoint sets have no elements in common, hence their intersection is the empty set (Ø).