Just to be sure, is that really for the second term in the denominator?
For the numerator:
You could use the rational roots theorem, which states that if the given polynomial has a rational root, it will come from the list . We can see that cannot work, hence we find:
So, we know is a factor of . Use of division finds:
Now, for the denominator, we should recognize the binomial coefficients arising from the cube of a binomial, i.e.:
and so we may state: