Determine whether or not each of the definition of given below gives a binary operation. In the event that * is not a binary operation, give justification for this.
(i) On Z+, define by a b = a − b
(ii) On Z+, define by a b = ab
(iii) On R, define by a b = ab2
(iv) On Z+, define by a b = |a − b|
(v) On Z+, define by a b = a
