4MA1/1H Jun 2022, Question 18: Choosing Between Sine and Cosine Rules
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1H (Higher) · Calculator · 5 marks
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The question, in short
Triangle ABC has AB = 9.7 m, BC = 12.3 m and angle ABC = 115°. Work out the value of angle BCA, labelled x, giving the answer to 3 significant figures.
Summarised in our own words. Use the official paper for the exact wording and the diagram.
Solution · 5 marks
- 1Cosine rule: AC² = 9.7² + 12.3² − 2 × 9.7 × 12.3 × cos 115° = 346.2…
- 2AC = 18.60…
- 3Sine rule: sin x = 9.7 × sin 115° ÷ 18.60… = 0.4725…
- 4x = 28.2
Answer28.2
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