4MA1/1H Jun 2019, Question 18: The Cosine Rule
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1H (Higher) · Calculator · 3 marks
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The question, in short
Using triangle PQR with PQ = 17.8 cm, RQ = 26.3 cm and angle PQR = 36°, calculate PR, giving the answer to 3 significant figures.
Summarised in our own words. Use the official paper for the exact wording and the diagram.
Solution · 3 marks
- 1Cosine rule: PR² = 17.8² + 26.3² − 2 × 17.8 × 26.3 × cos 36°
- 2PR² = 316.84 + 691.69 − 757.47… = 251.06…
- 3PR = √251.06… = 15.84…, which is 15.8
Answer15.8
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