Show that 1−cos4x1+cos4x≡tan22x\displaystyle \frac{1 - \cos 4x}{1 + \cos 4x} \equiv \tan^2 2x1+cos4x1−cos4x≡tan22x
Hence solve, for −π≤x≤π-\pi \leq x \leq \pi−π≤x≤π,
1−cos4x1+cos4x=1 \frac{1 - \cos 4x}{1 + \cos 4x} = 1 1+cos4x1−cos4x=1348 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.