4MA1/2F Jun 2019, Question 17: Finding Missing Sides
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2F (Foundation) · Calculator · 4 marks
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The question, in short
Similar triangles ABC and DEF are given with AB = 6 cm, AC = 4.2 cm, DE = 15 cm, EF = 19.5 cm; find DF and BC using corresponding sides.
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Part (a) · 2 marks
Use the similarity of the triangles to work out the length of DF in centimetres.
- 1AB corresponds to DE: scale factor = 15 ÷ 6 = 2.5
- 2AC corresponds to DF
- 3DF = 4.2 × 2.5 = 10.5
Answer10.5
Part (b) · 2 marks
Use the similarity of the triangles to work out the length of BC in centimetres.
- 1Scale factor = DE ÷ AB = 15 ÷ 6 = 2.5
- 2BC matches EF, so divide EF by the scale factor.
- 3BC = 19.5 ÷ 2.5 = 7.8
Answer7.8
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