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An equivalence relation $R$ on set $A = \{1, 2, 4\}$ must be reflexive, symmetric, and transitive. Reflexivity requires $(1,1), (2,2), (4,4) \in R$.
We are given $(1,2) \in R$ and $(2,1) \in R$. By symmetry, these are already satisfied. By transitivity, since $(1,2) \in R$ and $(2,1) \in R$, we must have $(1,1) \in R$ and $(2,2) \in R$, which are already covered by reflexivity.
Equivalence relations correspond to partitions of the set. The element $4$ can either be in a singleton set $\{4\}$ or grouped with $\{1, 2\}$.
Case 1: Partition is $\{\{1, 2\}, \{4\}\}$. The relation is $R_1 = \{(1,1), (2,2), (4,4), (1,2), (2,1)\}$. This satisfies all conditions.
Case 2: Partition is $\{\{1, 2, 4\}\}$. The relation is the universal relation $R_2 = A \times A$. This contains $(1,2)$ and $(2,1)$ and is an equivalence relation.
Final Answer: 2
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