Question

X∈R is equivalent to :

Answer 1

The equivalence classes for this relation are determined by the smallest elements; hence there are ten equivalence classes. The number of elements in the equivalence class {2,6,7} is the number of subsets of X that: first, contain 2; and second, all their other elements (if any) are from {3,4,5,6,7,8,9,10}.