Find all values of θ , between 0 & π, which satisfy the equation cosθcos2θcos3θ = 1/4
a. 0, π/8, π/3, 3π/8, 5π/8, 2π/3, 7π/8, π.
b. π/8, π/3, 3π/8, 5π/8, 2π/3, 7π/8.
c. π/8, π/3, 3π/8, 5π/8, 7π/8.
d. 0, π/8, 3π/8, 5π/8, 7π/8, π.