Hi, eniuqvw!

Obviously, all that is needed is to show that can be factored into the square of a quadratic in . If you can factor this expression right away, then good for you! I, however, didn't have much luck (if anyone has a nice and simple way to factor this, let me know!), so I worked backwards:

The square of a quadratic will have the form

So, if can indeed be factored as the square of a quadratic in , then it should take that form. With this assumption, we have:

Solving this, we find that .

And, indeed, if you try expanding it yourself, you will see that

And this fact should give you what you need to complete your proof.