You may use the identity cos3θ≡4cos3θ−3cosθ\cos 3\theta \equiv 4\cos^3\theta - 3\cos\thetacos3θ≡4cos3θ−3cosθ.
Show that the equation 1−cos3x=sin2x1 - \cos 3x = \sin^2 x1−cos3x=sin2x can be written as
cosx(4cosx+3)(cosx−1)=0\cos x\left(4\cos x + 3\right)\left(\cos x - 1\right) = 0cosx(4cosx+3)(cosx−1)=0
Hence solve, for −π≤x≤π-\pi \leq x \leq \pi−π≤x≤π, the equation
1−cos3x=sin2x1 - \cos 3x = \sin^2 x1−cos3x=sin2x
Give your answers to three significant figures where they are not exact.