The number of relations, on the set {1, 2, 3} containing (1,2) and (2, 3) which are reflexive and transitive but not symmetric, is_________.
Text Solution
Verified by Experts4
(4)
Given,
Set A = {1,2,3}
Now Cartesian product A x A = {(1,1), (2, 1), (1, 2), ........, (3,3)}
Now, given the relation is reflexive,
So, (1, 1), (2, 2), (3, 3)
R
Also given (1, 2), (2, 3)
R, (1,3) must
R
Now finding, Possible cases:
Case-l: All of (2, 1), (3, 2), (3, 1)
R
1 relation.
Case-2: Only one of (2, 1), (3, 2), (3, l)
R
3 relations.
For example if relation is {(1, 1), (2, 2), (3, 3),(2,1)} then it is reflexive as well as transitive as (2, 2),(2,1)
(2,1) is present in relation
Note that exactly two of (2, 1), (3, 2), (3,1)
R is not possible because if two of these
R, third must
R to make relation transitive.
Total number of relations = 4
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