Show that *,defined on Q (where Q is a set of rational numbers) by

a * b = a + b + 3ab

is a commutative binary operation.Is is associative?

Ive answered this part but i dont know how to answer part b

Determine the identity element admitted by * and show that it is unique.Show that with respect to this identity the inverse a(^ -1) of a is given by

a(^ -1) = ((-a)/(1+3a))

Give an element a C Q which has no inverse with respect to *.

(where C means contained, Q is a set of rational numbers)