Consider the relation R on the set \-2, -1, 0, 1, 2\ defined by (a, b) R if and only if 1+ab>0. Then, among the statements :
- Only I is true
- Only II is true
- Both I and II are true
- Neither I nor II is true
Answer
(1) Only I is true
Solution
1+a a=1+a2>0 for every a (a, a) : R is reflexive
1+ab=1+ba R is symmetric
1+ab 0 ab -1, i.e. a, b non-zero and of opposite signs
a \1, 2\, b \-1, -2\ or a \-1, -2\, b \1, 2\: 4+4=8 pairs are not in R
n(R)=5 5-8=17 Statement I is true
(2, 0) and (0, -2) ( 1+0>0)
But 1+2(-2)=-3<0 (2, -2) R is not transitive
R is not an equivalence relation Statement II is false
Answer: (1)