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4MA1/2H Jun 2019, Question 6: Finding Missing Sides

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2H (Higher) · Calculator · 4 marks

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The question, in short

Using two similar triangles ABC and DEF with AB = 6 cm, AC = 4.2 cm, DE = 15 cm and EF = 19.5 cm, find the unknown side lengths DF and BC.

Summarised in our own words. Use the official paper for the exact wording and the diagram.

Part (a) · 2 marks

Find the length of DF using the scale factor between the similar triangles.

  1. 1AB matches DE: scale factor = 15 ÷ 6 = 2.5
  2. 2DF matches AC: DF = 4.2 × 2.5 = 10.5

Answer10.5

Part (b) · 2 marks

Find the length of BC using the scale factor between the similar triangles.

  1. 1Scale factor = DE ÷ AB = 15 ÷ 6 = 2.5
  2. 2BC matches EF, so divide EF by the scale factor.
  3. 3BC = 19.5 ÷ 2.5 = 7.8

Answer7.8

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