a. By writing 3 as 2 + , show that cos 3 4 cos 3

a. By writing 3θ as 2θ + θ, show that cos 3θ ≡ 4 cos³ θ − 3 cos θ.

b. Hence, or otherwise, for 0 < θ < π, solve 6 cos θ − 8 cos³ θ + 1 = 0 giving your answer in terms of π.