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Case study·Hard exam skill (4/5)·No calculatorNeeds mentor review

Difficulty guide

The label describes the problem, not your ability.

1/5 - Foundational

Warm-up setup; checks one basic idea.

2/5 - Routine exam skill

Normal syllabus skill; usually one main rule or interpretation.

3/5 - Standard multi-step

Exam-style problem with multiple steps or a common trap.

4/5 - Hard exam skill

High-end exam problem; combines methods carefully.

5/5 - Challenge

Stretch problem beyond normal exam pressure.

Question

Let xx be acute with sin⁡x=35\sin x=\frac35 and cos⁡x=45.\cos x=\frac45.
Total: 4 marks

(a) Find sin⁡2x\sin2x. (1 mark)

(b) Find cos⁡2x\cos2x. (1 mark)

(c) Find sin⁡3x\sin3x. (1 mark)

(d) A learner claims sin⁡3x=3sin⁡x\sin3x=3\sin x. Decide whether the claim is correct, and justify. (1 mark)

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cbse-math-11.u1.t1-9.case.005

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