Which of the following are examples of the null set?
D = {x : x ϵ N, x2 + 1 = 0}.
Natural numbers = 1, 2, 3, 4, 5, 6,…
If x = 1, then x2 + 1 = (1)2 + 1 = 1 + 1 = 2 ≠ 0
∴ no elements in the set B because the equation 2x + 3 = 4 is not satisfied by any natural number of x.
∴ It is a null set.