Use the identity for sin(A+B)\sin(A + B)sin(A+B) to express sin2A \sin 2A\,sin2A in terms of sinA \sin A\,sinA and cosA\cos AcosA.
Use the identity for cos(A+B)\cos(A + B)cos(A+B) to express cos2A \cos 2A\,cos2A in terms of sinA \sin A\,sinA and cosA\cos AcosA.
Hence, express cos2A \cos 2A\,cos2A in terms of cosA\cos AcosA.
Hence, express cos2A \cos 2A\,cos2A in terms of sinA\sin AsinA.
Use the identity for tan(A+B)\tan(A + B)tan(A+B) to express tan2A \tan 2A\,tan2A in terms of tanA\tan AtanA.
317 exam-style questions on AQA A Level Maths 1.8 E: Trigonometry, covering 1.8.1 Trigonometric definitions, rules and radians, 1.8.2 Small angle approximations (A-level only), 1.8.3 Trigonometric functions and exact values, 1.8.4 Reciprocal and inverse trigonometric functions (A-level only), 1.8.5 Trigonometric identities, 1.8.6 Compound and double angle formulae (A-level only), 1.8.7 Solving trigonometric equations, 1.8.8 Proofs with trigonometric identities, and 1.8.9 Trigonometry in context. Each one has a worked solution and a mark scheme showing where the marks go.