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A-LevelMathematicsComplex numbers9709/33 · Oct/Nov 2019 · Q67 Marks

Throughout this question the use of a calculator is not permitted. The complex number with modulus 1 and argument 1/3π is denoted by w. The complex number 1 + 2i is denoted by u. The complex number v is such that |v| = 2|u| and arg v = arg u + 1/3π.

  1. (i)Express w in the form x + iy, where x and y are real and exact.[1]
  2. (ii)Sketch an Argand diagram showing the points representing u and v.[2]
  3. (iii)Explain why v can be expressed as 2uw. Hence find v, giving your answer in the form a + ib, where a and b are real and exact.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

  1. [B1] Obtain answer w = 1/2 + i√3/2
  2. [B1] Show point representing u
  3. [B1] Show point representing v in relatively correct position
  4. [B1] Explain why the moduli are equal
  5. [B1] Explain why the arguments are equal
  6. [M1] Use i² = -1 and obtain 2uw in the given form
  7. [A1] Obtain answer 1 - 2√3 + (2 + √3)i

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About this question

Topic
Complex numbers, A-Level Mathematics (syllabus 9709). Structured question, 7 marks.
Source
A-Level Mathematics, Oct/Nov 2019 Paper 3 Variant 3, question 6.

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