Hai,

I have some toubles with this question.

Define an operator * on $\displaystyle R$ by

$\displaystyle x*y = 2xy -x -y $

a) is * commutative?

b) is * associative?

I can easily see that * is commutative, but how do i test for associativity?

The rule states that (x*y)*z = x*(y*z)

But what is z ?