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Edexcel IAL Mathematics P3.2.3 compound angles and R-form

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.

Syllabus
First assessment 2019
Course
Mathematics YMA01
Level
A2

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.

P3.2.3 - Knowledge question 1

[Maximum number: 2]

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

cos⁡2A≡2cos⁡2A−1\cos 2 A \equiv 2 \cos ^{2} A-1
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