I don't understand how to prove that a relation is an equivalence relation. Here is the problem:

Let A be the set of all statement forms in three variables p, q and r. R is the relation defined on A as follows: For all P and Q in A,

P R Q <=> P and Q have the same truth table.

I am supposed to a) prove that the relation is an equivalence relation, and b) describe the distinct equivalence classes of each relation.

Can anyone tell me how to get started?