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A-LevelMathematicsSeries9709/12 · Oct/Nov 2018 · Q14 Marks

Find the coefficient of 1/x² in the expansion of (3x + 2/(3x²))⁷.

  1. (a)Find the coefficient of 1/x² in the expansion of (3x + 2/(3x²))⁷.[4]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

  1. [B1] For a correctly selected term in x⁻² : (3x)⁴ or 3⁴
  2. [B1] * (2/(3x²))³ or (2/3)³
  3. [B1] × ⁷C₃ or ⁷C₄
  4. [B1] → 840 or 840/x²

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About this question

Topic
Series, A-Level Mathematics (syllabus 9709). Structured question, 4 marks.
Source
A-Level Mathematics, Oct/Nov 2018 Paper 1 Variant 2, question 1.

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