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A-LevelFurther MathematicsProof by induction9231/12 · May/June 2022 · Q38 Marks

The sequence of positive numbers u₁, u₂, u₃, … is such that u₁ > 4 and, for n ≥ 1, uₙ₊₁ = (uₙ²+uₙ+12)/(2uₙ).

  1. (a)By considering uₙ₊₁-4, or otherwise, prove by mathematical induction that uₙ > 4 for all positive integers n.[5]
  2. (b)Show that uₙ₊₁ < uₙ for n ≥ 1.[3]

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

  1. [B1] States base case.
  2. [B1] States inductive hypothesis.
  3. [M1] Considers u_(k+1)-4, puts over common denominator.
  4. [A1]
  5. [A1]
  6. [M1 A1] Considers uₙ₊₁-uₙ.
  7. [A1] Uses uₙ > 4.

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About this question

Topic
Proof by induction, A-Level Further Mathematics (syllabus 9231). Structured question, 8 marks.
Source
A-Level Further Mathematics, May/June 2022 Paper 1 Variant 2, question 3.

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