Let A=\1,2,3\. The number of relations on A, containing (1,2) and (2,3), which are reflexive and transitive but not symmetric, is .
Answer
3
Solution
Reflexive: (1,1),(2,2),(3,3); given (1,2),(2,3) and transitive (1,3) (black dots)
[figure]
(3,1) forces (3,2),(2,1) R=A A (symmetric) ✗
(3,2) with (2,1) forces (3,1) ✗
Allowed: none of them, only (2,1), only (3,2)
number of relations =3
Answer: 3