Hey! I have a problem here that I can't solve, help would be greatly appreciated. 1. The problem statement, all variables and given/known data In a triangle ABC with sides a, b and c, B is 60°. Use the cosinus law to prove this formula: http://www4c.wolframalpha.com/Calculate/MSP/MSP54721a0508eiidf5ddbd00005aahbcg10134ag4h?MSPStoreType=image/gif&s=34&w=147&h=47 [Broken] 2. The attempt at a solution I have no idea how to solve this so I was hoping you guys could at least point me in the right direction. -Thanks in advance!