The domain and codomain of the following three functions (i.e., fi(), f2() and f3()) are A and B respectively, where A = R x R and B = R. Determine whether each of the following functions is injective and/or surjective. (Steps required.) (a) fi((a,b)) =a+b (b) f((a,b))=a2-5 (c) f((a,b))=([b]-[b])+([a]-[a]) Prove by contradiction, or disprove, the following two statements. (a) 5 is irrational. (b) For any non-empty binary relation R on the set A = {a, b, c, d}, if R is reflexive, transitive and antisymmetric, then R is not symmetric. (To prove by contradiction, the assumption should be written down clearly.)