A mechanical engineer models the efficiency, EEE, of a specialized turbine using the function
E(θ)=4cos2θ+2cosθ+6 E(\theta) = 4 \cos 2\theta + 2 \cos \theta + 6 E(θ)=4cos2θ+2cosθ+6where θ \theta\,θ is the blade pitch angle in degrees.
Find all values of θ\thetaθ, for 0≤θ<360∘0 \le \theta < 360^\circ0≤θ<360∘, for which the efficiency is exactly 5. Give your solutions to one decimal place where appropriate.
(Solutions based entirely on graphical or numerical methods are not acceptable.)
