Let \( R_1 \) and \( R_2 \) be two relations defined on \( \mathbb{R} \) by \( a \, R_1 \, b \Leftrightarrow ab \ge 0 \) and \( a \, R_2 \, b \Leftrightarrow a \ge b \). Then:
\( R_1 \) is an equivalence relation but not \( R_2 \)
\( R_2 \) is an equivalence relation but not \( R_1 \)
Both \( R_1 \) and \( R_2 \) are equivalence relations
Neither \( R_1 \) nor \( R_2 \) is an equivalence relation