(2 pts) Let \mathbb{R} be the set of all real numbers and consider the following relations on \mathbb{R}. For each one, determine whether it is reflexive on \mathbb{R}, symmetric and transitive. Justify each answer with an argument. \begin{align*} R_1 &= \{(x, y) \in \mathbb{R} \times \mathbb{R} : x^2 + y^2 = 1\} \\ R_2 &= \{(x, y) \in \mathbb{R} \times \mathbb{R} : xy \neq 0\} \\ R_3 &= \{(x, y) \in \mathbb{R} \times \mathbb{R} : |x - y| < 5\} \\ R_4 &= \{(x, y) \in \mathbb{R} \times \mathbb{R} : x \ge y\} \end{align*}
