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0606/11 Oct/Nov 2025, Question 12: Vector Proofs

Cambridge IGCSE Additional Mathematics 0606 · Paper 11 (Non-calculator) · Non-calculator · 6 marks

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The question, in short

Given position vectors OA = (1, 7), OB = (7, 4) and OC = k(1, 2), with C on line AB, use vectors to find the ratio AC : AB.

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

Solution · 6 marks

  1. 1AB = (7, 4) − (1, 7) = (6, −3)
  2. 2AC = k(1, 2) − (1, 7) = (k − 1, 2k − 7)
  3. 3AC parallel to AB: (k − 1)/6 = (2k − 7)/(−3)
  4. 4−3k + 3 = 12k − 42 ⇒ k = 3
  5. 5AC = (2, −1) = (1/3)AB
  6. 6AC : AB = 1 : 3

AnswerAC : AB = 1 : 3

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