Question:
Check whether the relation R defined on the set A = {1, 2, 3, 4, 5, 6} as R = {(a, b) : b = a + 1} is reflexive, symmetric or transitive.
Solution:
Reflexivity:
Let $a$ be an arbitrary element of R. Then,
$a=a+1$ cannot be true for all $a \in A$
$\Rightarrow(a, a) \notin R$
So, $R$ is not reflexive on $A$.
Symmetry:
Let $(a, b) \in R$
$\Rightarrow b=a+1$
$\Rightarrow-a=-b+1$
$\Rightarrow a=b-1$
Thus, $(b, a) \notin R$
So, $R$ is not symmetric on $A$.
Transitivity:
Let $(1,2)$ and $(2,3) \in R$
$\Rightarrow 2=1+1$ and $32+1$ is true.
But $3 \neq 1+1$
$\Rightarrow(1,3) \notin R$
So, $R$ is not transitive on $A$.