I figured it out:

We will show each set is a subset of the other:

elements of ( , ) have the form (a+b ) + (c+d )

let q be an element of ( + ) then q has the form:

q = a + b( + ) = a + b +b which is of the form mentioned above with a=a, b=b, c=0, d=b. Therefore ( + ) is a subset of ( , )

Now consider ( + )^3 = 11 + 9 ( I did the math)

subtract 9( + ) from both sides and you get:

2 = ( + )^3 - 9( + ) so is an element of ( + ) similar procedure can show that is also an element of that set and therefore ( , ) is a subset of ( + )

So the sets are the same