Relation from set A to B: subset of A × B (Cartesian product). Notation: R ⊆ A × B. If (a,b) ∈ R, say a R b. Cartesian product A × B = {(a,b) | a ∈ A, b ∈ B}. Example: A = {1,2}, B = {a,b}. A × B = {(1,a), (1,b), (2,a), (2,b)}. Relation R = {(1,a), (2,b)} is one possible relation. Domain of R = first elements {1, 2}; Range = second elements {a, b}. Representation: (1) Ordered pairs; (2) Ordered diagram; (3) Table; (4) Graph. Solving: Identify domain and range from relation. Verify if ordered pairs satisfy relation definition. Exam tip: Understand A × B ≠ B × A. Count total possible relations: 2^(|A| × |B|).