(Binary Operation) Show that :

Question

Show that : 

• * On Z⁺ defined by a*b=ab is binary operation.
• * On Z⁺ defined by a*b=|a-b| is not a binary operation.
• * On Z⁺ defined by a*b=a-b is a binary operation.
• * On Q defined by a*b=ab/2 is a binary operation.
• * On R defined by a*b=ab² is a binary operation.