4MA1/1H Jan 2021, Question 16: Bearings with 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
Using a diagram with AB = 150 m, AC = 275 m and bearing of C from A equal to 120°, find the bearing of C from B to the nearest degree.
Summarised in our own words. Use the official paper for the exact wording and the diagram.
Solution · 5 marks
- 1BC² = 150² + 275² − 2 × 150 × 275 × cos 120° = 139 375
- 2BC = √139 375 = 373.3…
- 3Sine rule: sin B = 275 × sin 120° ÷ 373.3… = 0.6379…
- 4Angle ABC = 39.6…°
- 5Bearing of C from B = 180 − 39.6… = 140.4…, so 140
Answer140
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