Consider the relations $R_1$ and $R_2$ defined as $a R_1 b \Leftrightarrow a^2 + b^2 = 1$ for all $a, b \in \mathbb{R}$ and $(a,b) R_2 (c,d) \Leftrightarrow a + d = b + c$ for all $a, b, c, d \in \mathbb{N} \times \mathbb{N}$. Then\\
(1) Only $R_1$ is an equivalence relation\\
(2) Only $R_2$ is an equivalence relation\\
(3) $R_1$ and $R_2$ both are equivalence relations\\
(4) Neither $R_1$ nor $R_2$ is an equivalence relation