Q: Use an appropriate compound angle formula to determine an exact value for $\displaystyle cos(11pi/12)$

I know that you have to express the angle as a sum/difference of two special angles. In this case, cos(165) = cos(45 + 120). I get stuck here. Does this mean I have to break down 120 into (60 + 60)? :/

any sort of help/hints would be greatly appreciated.