4MA1/1F Jan 2019, Question 19: Choosing the Right Trigonometric Ratio
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1F (Foundation) · Calculator · 5 marks
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The question, in short
Triangle ACD has B on straight line AC, right angle ABD, angle ADB 20°, DB 12.6 cm and DC 19.3 cm. Work out length AC to 1 decimal place.
Summarised in our own words. Use the official paper for the exact wording and the diagram.
Solution · 5 marks
- 1Triangle ABD: tan 20° = AB/12.6, so AB = 12.6 × tan 20° = 4.586…
- 2Triangle DBC (Pythagoras): BC² = 19.3² − 12.6² = 213.73
- 3BC = √213.73 = 14.619…
- 4AC = AB + BC = 4.586… + 14.619… = 19.205… = 19.2
Answer19.2
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