Answer: An equivalence relation with 2 classes.
- A Not reflexive, since a + a may be odd
- B Symmetric but not transitive
- C An equivalence relation with infinitely many classes
- D An equivalence relation with 2 classes
Correct answer: D. An equivalence relation with 2 classes
Explanation: a + a = 2a is always even so it is reflexive, addition is symmetric, and transitivity holds - the classes are the evens and the odds.
Concept context
Types of relations, equivalence classes, one-one and onto functions, composition, and invertible functions