What is [0] and [1] for a,b (belong to) Z if and only if a^2-b^2 is divisible by 3?

Question

I need to know the answer as well as understand this.

Any help will be appreciated very very much, and it is urgent.

[0] implies the set that contains 0 and [1] implies the set that contains [1]. However, I already turned in my homework so I don't really care about this problem anymore

Answer 1

What do you mean by [0] and [1]?