Which of the following is not an equivalence relation on Z?
(a) a R b ⇔ a + b is an even integer
(b) a R b ⇔ a − b is an even integer
(c) a R b ⇔ a < b
(d) a R b ⇔ a = b
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Solution
(c) a R b ⇔ a < b
Clearly, R is not a symmetric relation. This is because if (a, b) is an element of relation R, then, a < b does not imply b < a a, b Z.
Hence, R is not an equivalence relation on Z.