Consider the relations R1 and R2 defined as a R1 b a2+b2=1 for all a, b R and (a, b) R2(c, d) a+d=b+c for all (a, b),(c, d) N N. Then :
- R1 and R2 both are equivalence relations
- Only R1 is an equivalence relation
- Only R2 is an equivalence relation
- Neither R1 nor R2 is an equivalence relation
Answer
(3) Only R2 is an equivalence relation
Solution
R1: 12+12=2 1 (1,1) R1 R1 is not reflexive not an equivalence relation
R2: a+b=b+a (a,b)R2(a,b) reflexive
a+d=b+c c+b=d+a (c,d)R2(a,b) symmetric
a+d=b+c and c+f=d+e; adding a+f=b+e transitive
Only R2 is an equivalence relation
Answer: (3)