4MA1/2F Nov 2021, Question 26: Choosing the Right Trigonometric Ratio
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2F (Foundation) · Calculator · 4 marks
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The question, in short
In isosceles triangle ABC with BA = BC, N lies on AC with AN = 9.3 cm, BN perpendicular to AC, and angle BAC = 38°. Find the perimeter of ABC to 3 significant figures.
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Solution · 4 marks
- 1Triangle ABN is right-angled at N: cos 38° = 9.3/AB
- 2AB = 9.3 ÷ cos 38° = 11.80… cm, and BC = AB
- 3AC = 2 × 9.3 = 18.6 cm
- 4Perimeter = 11.80… + 11.80… + 18.6 = 42.2 cm
Answer42.2
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