I need help in equivalence relationship...

Question> For points (x1, y1) and (x2, y2) in a plane with rectangular

coordinate system, let (x1, y1) ~ (x2, y2) mean that either x1=x2 or y1=y2.

i) Explain why ~ is not an equivalence relation on the set of points in the

plane.

ii) And describe the equivalence classes geometrically..And give a complete

set of equivalence class representatives.

Thank you!