Show that cos3θ≡4cos3θ−3cosθ\cos 3\theta \equiv 4 \cos^3 \theta - 3 \cos \thetacos3θ≡4cos3θ−3cosθ
Hence, solve, for −π≤θ≤π-\pi \leq \theta \leq \pi−π≤θ≤π,
1−cos3x=sin2x 1 - \cos 3x = \sin^2 x 1−cos3x=sin2x137 exam-style questions on Edexcel A Level Maths Trigonometry and Modelling, covering 7.1 Addition Formulae, 7.2 Double Angle Formulae, 7.3 Solving Trigonometric Equations, 7.4 Simplifying a cos x +- b sin x, 7.5 Proving Trigonometric Identities, and 7.6 Modelling with Trigonometric Functions. Each one has a worked solution and a mark scheme showing where the marks go.