Yes, you are correct so far, now what you want to do is factor.
I've attempted this, and a number of other problems from the Stewart calculus book, 2.5 #17.
I think I Have the right answer so far, but I've no idea how to factor something so complex. I've looked over the answer, and an example in the book, but can't work out what they are doing. I'd really appreciate some help, but given that I have no idea what I need to be doing here, I might need more than just a small tip.