Test whether the following relations R1, R2 and R3 are (i) reflexive (ii) symmetric and (iii) transitive :
R1 on Q0 defined by (a, b) ϵ R1⇔ a = 1/b
Here, R1, R2, R3, and R4 are the binary relations.
So, recall that for any binary relation R on set A. We have,
R is reflexive if for all x ∈ A, xRx.
R is symmetric if for all x, y ∈ A, if xRy, then yRx.
R is transitive if for all x, y, z ∈ A, if xRy and yRz, then xRz.
So, using these results let us start determining given relations.
We have
R1 on Q0 defined by (a, b) ∈ R1⇔
Check for Reflexivity:
∀ a, b ∈ Q0,
(a, a), (b, b) ∈ R1 needs to be proved for reflexivity.
If (a, b) ∈ R1
Then, …(1)
So, for (a, a) ∈ R1
Replace b by a in equation (1), we get
But, we know
⇒ (a, a) ∉ R1
So, ∀ a ∈ Q0, then (a, a) ∉ R1
∴ R1 is not reflexive.
Check for Symmetry:
If (a, b) ∈ R1
Then, (b, a) ∈ R1
∀ a, b ∈ Q0
If (a, b) ∈ R1
We have, …(2)
Now, for (b, a) ∈ R1
Replace a by b & b by a in equation (2), we get
⇒ (b, a) ∈ R2
So, if (a, b) ∈ R1, then (b, a) ∈ R1
∀ a, b ∈ Q0
∴ R1 is symmetric.
Check for Transitivity:
If (a, b) ∈ R1 and (b, c) ∈ R1
We need to eliminate b.
We have
Putting in
, we get
But,
⇒ (a, c) ∉ R1
So, if (a, b) ∈ R1 and (b, c) ∈ R1, then (a, c) ∉ R1
∀ a, b, c ∈ Q0
∴ R1 is not transitive.