UPSC NDA Math Model Paper 8

Given A = {3, 7}, B = {5, 11}
Cartesian product A × B = {(3, 5), (3, 11), (7, 5), (7, 11)}
Relation R = {(a, b): a ∈ A, b ∈ B and a + b is even}
Roster form R = {(3, 5), (3, 11), (7, 5), (7, 11)}
R‌−1 = {(5, 3), (11, 3), (5, 7), (11, 7)}
Inverse relation R‌−1 = {(3, 5), (3, 11), (7, 5), (7, 11)} = A × B
Hence relation R‌−1 is universal relation