Equivalence Classes with 1 or 2 elements?

Question

6. Let ~ be the relation on $\mathbb R$ defined by
   a ~ b if and only if |a| = |b|:

(a) Prove that is an equivalence relation.
(b) Give an example of an equivalence class with two elements.
(c) Give an example of an equivalence class with one element.
(d) Give a complete set of equivalence class representatives.

I can do part (a) of the question by showing the symmetry, reflexivity and transitivity but I'm struggling with the rest of the question. Can anyone give me some hints?

Answer 1

Hint: Your equivalence class is $\pm a$ for some number $a$. So give an example where $+a \neq -a$ and give an example where $+a = -a$.