Each of the following defines a relation on N:
x is greater than y, x, y ∈N
Determine which of the above relations are reflexive, symmetric and transitive.
Let R = {(x,y): x is greater than y ∀ x,y ∈ N } be a relation defined on N.
Now,
We observe that, any element x ∈ N cannot be greater than itself.
⇒ (x,x) ∉ R ∀ x ∈ N
⇒ R is not reflexive.
Let (x,y) ∈ R ∀ x, y ∈ N
⇒ x is greater than y
But y cannot be greater than x if x is greater than y.
⇒ (y,x) ∉ R
For e.g., we observe that (5,2) ∈ R i.e 5 > 2 but 2 ≯ 5 ⇒ (2,5) ∉ R
⇒ R is not symmetric
Let (x,y) ∈ R and (y,z) ∈ R ∀ x, y,z ∈ N
⇒ x > y and y > z
⇒ x > z
⇒ (x,z) ∈ R
For e.g., we observe that
(5,4) ∈ R ⇒ 5 > 4 and (4,3) ∈ R ⇒ 4 > 3
And we know that 5 > 3 ∴ (5,3) ∈ R
⇒ R is transitive.
Thus, R is transitive but not reflexive not symmetric.