Question

An operation is defined on the set of real numbers, R by x*y = x+y+3xy. If * is commutative, find the value x is an element of R for which no inverse exists

Answer 1

if y is x inverse, then x*y = 1
y = (1-x)/(1+3x)
so x = -1/3 has no inverse

Answer 2

I really don't understand