(1+4xsin666) squared is approx. 5. You should go to quizzes and puzzles and search for answers to ev776, this is where everyone is discussing the puzzle - it's a beast!
Thank you Physicsgirl - I reposted this question on Q & P, and someone pointed me in the direction of this link. I wish I'd found it earlier .... I thought I'd looked for one quite thoroughly and can't think how I missed it !