Well, it helps to know what an equivalence relationis!

aRb, on set X, is an equivalence relation if and only if it

1) is reflexive: aRa for every a in X. Is it true that f(a)= f(a) for all a in X?

2) is symmetric: if aRb then bRa. Is it true thatiff(a)= f(b) then f(b)= f(a)?

3) is transitive: if aRb and bRc then aRc. Is it true thatiff(a)= f(b) and f(b)= f(c) then f(a)= f(c)?

(This is an easy problem because it involves "=" and "=" is the epitome of equivalence relations.)