Let R be a relation on N × N defined by (a, b) R (c, d) if and only if ad = bc. This relation is:

Let R be a relation on N × N defined by (a, b) R (c, d) if and only if ad = bc. This relation is:

• A. Reflexive only
• B. Symmetric only
• C. An equivalence relation
• D. None of these

Answer: C) An equivalence relation

Explanation: Just like a+d=b+c represents a-b = c-d, ad=bc represents a/b = c/d (since N has no zeros). Equality of fractions is reflexive, symmetric, and transitive, making it an equivalence relation.