Question

Find cosπ/12 and 7π/12 using the known values of sine cosine and tan of π/3 and π/4

Answer 1

since π/12 = π/3 - π/4, just use the sum/difference formulas:

cos π/12 = cos π/3 cos π/4 + sin π/3 sin π/4
cos 7π/12 = cos π/3 cos π/4 - sin π/3 sin π/4