S × S = {,,,,} R A-D = C-B < = > A+B = C+D, two ordered pairs have a relationship R as long as the sum of the two elements is equal, so R obviously satisfies reflexivity, symmetry and transitivity, so R is equivalent. According to the definition of R, as long as the sum of two elements of two ordered pairs is equal, two ordered pairs are in the same equivalence class. The sum of two elements of an ordered pair in S×S can only be 4, 5, 6, 7, 8. The sum of 4 is: while 5 is:, 6 is:, 7 is:, and 8 is: so the quotient set A/R = {}, {,}, {}, {}.