Let R be a relation on Z Z defined by (a, b)R(c, d) if and only if ad-bc is divisible by 5. Then R is
- Reflexive and transitive but not symmetric
- Reflexive and symmetric but not transitive
- Reflexive but neither symmetric nor transitive
- Reflexive, symmetric and transitive
Answer
(2) Reflexive and symmetric but not transitive
Solution
Reflexive: ab-ba=0, divisible by 5 (a,b)R(a,b)
Symmetric: 5 (ad-bc) 5 (cb-da) (c,d)R(a,b)
Transitive: (3,1)R(10,5) ∵ 3 5-1 10=5
and (10,5)R(1,1) ∵ 10 1-5 1=5
but 3 1-1 1=2 (3,1) is not related to (1,1) not transitive
∴ R is reflexive and symmetric but not transitive
Answer: (2)