0606/21 Oct/Nov 2025, Question 13: Solving Trig Equations
Cambridge IGCSE Additional Mathematics 0606 · Paper 21 (Calculator) · Calculator · 6 marks
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The question, in short
Solve 2 sin³θ = 3 sin θ cos θ for θ in the interval −π/2 ≤ θ ≤ π/2, giving all solutions.
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Solution · 6 marks
- 1sin θ(2 sin²θ − 3 cos θ) = 0
- 2sin θ = 0 gives θ = 0
- 32(1 − cos²θ) = 3 cos θ
- 42 cos²θ + 3 cos θ − 2 = 0
- 5(2 cos θ − 1)(cos θ + 2) = 0; cos θ = −2 has no solution
- 6cos θ = 1/2 gives θ = ±π/3
Answerθ = 0, θ = ±π/3 (±1.05)
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Also searched as: 0606/21/O/N/25 · 0606_w25_qp_21 · 0606 w25 21 · question 13.
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