I have another similar question which i am stucked half way through. I applied the same technique to it as in the other thread:

Prove that is a root of the equation

Let where

Since , it follows that **

Let be Q and be P

--- 1

This is where i am stucked, i tried to form the second equation from ** but there are 3 extra terms which give me P+Q+cos B1+ cos B7+ cosB8 and probably i will need more equations here since the roots of the weird square root equation will definitely be more than 2.