By writing cos3x \cos 3x\,cos3x as cos(2x+x)\cos(2x + x)cos(2x+x), show that cos3x=4cos3x−3cosx\cos 3x = 4\cos^3 x - 3\cos xcos3x=4cos3x−3cosx.
Solve, for 0≤x≤1800 \leq x \leq 1800≤x≤180, the equation,
4cos3x−3cosx=−0.65 4\cos^3 x - 3\cos x = -0.65 4cos3x−3cosx=−0.65Give your answers to 1 decimal place.
Practise Edexcel A Level Maths Trigonometry and Modelling with exam-style questions for A Level Maths. 100 questions 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, matched to the Edexcel A Level Maths (9MA0) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.