Edexcel Mathematics Sample paper · Paper 2 · Question 2 · ExamRizz

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Sample paper · Paper 2 · Question 2 · 3 marks

2. Some A level students were given the following question. Solve, for –90° < θ < 90°, the equation cos θ = 2 sin θ The attempts of two of the students are shown below. Student A Student B cos θ = 2 sin θ tan θ = 2 θ = 63.4° cos θ = 2 sin θ cos2 θ = 4 sin2 θ 1 – sin2 θ = 4sin2 θ θ= θ = ± θ ° = ± (a) Identify an error made by student A. (1) Student B gives θ = –26.6° as one of the answers to cos θ = 2 sin θ. (b) (i) Explain why this answer is incorrect. (ii) Explain how this incorrect answer arose.

Lesson: Proof by Deduction