Cho A = {11, 12, 13, 14, 15}. Trên A xác định quan hệ R như sau: ∀a,b ∈ A, aRb ⇔ a + b = 2k + 1 (k=1,2,...). Quan hệ R được biểu diễn là.

{(11, 12), (11, 14), (12, 13), (12, 15)}

{(11, 11), (12, 12), (13, 13), (14,14), (15,15), (11, 12), (11, 14), (12, 13), (12, 15)}

{(11, 12), (12, 11), (11, 14), (14, 11), (12, 15), (15, 12)}

{(11, 12), (12, 11), (11, 14), (14, 11), (12, 15), (15, 12), (13, 14), (14, 13), (12, 13), (13, 12), (14, 15), (15, 14)}