Let A = {1, 2, 3, 4}. Let R be the equivalence relation on A × A defined by (a, b)R(c, d) if a + d = b + c. Find the equivalence class [(1,3)].
L and M are two points with position vectors and respectively. Write the position vectors of a point N which divides the line segment LM in the ratio 2:1 externally.