Edexcel A-Level Mathematics A2 P3.2.3 Knowledge Questions

Questions combine identity proof and R-form work: rewrite sine-cosine combinations, find exact R and α, then use the form to locate extrema or solve angles.

Exam points

Express a sine-cosine combination as Rsin(2x − α) or Rcos(2x + α) with exact R and α.
Use R-form to find exact maximum or minimum values and when they first occur.
Apply double-angle, cosec or cot identities to prove equations before solving.

[Maximum number: 2]

Using the identity for $\cos (A+B)$ , prove that

\cos 2 A \equiv 2 \cos ^{2} A-1

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Edexcel A-Level Mathematics A2 P3.2.3 Knowledge Questions question 1