Given A = {1, 2}
B = {1, 2, 3, 4}
C = {5,6}
D = {5,6,7,8}
A x C = {1,2} x {5,6}
= {(1,5) (1,6) (2, 5) (2, 6)}
B x D = {1,2, 3, 4} x {5, 6, 7, 8}
= {(1,5) (1,6) (1,7) (1,8) (2, 5) (2, 6) (2,7) (2, 8) (3, 5) (3, 6) (3, 7) (3, 8) (4, 5) (4, 6) (4, 7) (4, 8)}
∴ A x C ⊂ B x D
Hence it is verified.