Let $N$ be the set of all natural numbers and $R$ be a relation on $N \times N$ defined by $(a, b) R (c, d) \Leftrightarrow ad = bc$ for all $(a, b), (c, d) \in N \times N$. Show that $R$ is an equivalence relation on $N \times N$. Also, find the equivalence class of $(2, 6)$, i.e., $[(2, 6)]$. [All India 2019, 2022]