1. The problem statement, all variables and given/known data Solve cos(3θ) = 0.85 in the range 0 ≤ θ ≤ 360° 2. Relevant equations 3. The attempt at a solution cos(3θ) = 0.85 3θ = 31.79° θ = 10.6° (3 s.f) I have drawn my transformed cos curve, where the full wave completes after 120°, so there are 3 full cycles in my range. I often make silly mistakes and i'm not sure of the best method to check my results. Using the symmetry of the curve I have calculated that θ = 10.6°, 109.4°, 130.6°, 229.4°, 250.6°, 349.4°. So, how do I verify these?