7) will mark brainliest + 10 points : )

Use the half angle identity: cos(A/2)=+/- √[(1+cosA)/2]
π/12 is half of π/6, and cosπ/6=√3/2, so
cons(π/12)=√[(1+√3/2)/2]=(1/2)√(2+√3)
C is the answer.