For each binary operation * defined below, determine whether * is commutative or associative. (i) On Z , define a * b = a − b (ii) On Q , define a * b = ab + 1 (iii) On Q , define a * b (iv) On Z + , define a * b = 2 ab (v) On Z + , define a * b = a b (vi) On R − {−1}, define