The sequence of positive numbers u₁, u₂, u₃, … is such that u₁ > 4 and, for n ≥ 1, uₙ₊₁ = (uₙ²+uₙ+12)/(2uₙ).
- (a)By considering uₙ₊₁-4, or otherwise, prove by mathematical induction that uₙ > 4 for all positive integers n.[5]
- (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.
- [B1] States base case.
- [B1] States inductive hypothesis.
- [M1] Considers u_(k+1)-4, puts over common denominator.
- [A1]
- [A1]
- [M1 A1] Considers uₙ₊₁-uₙ.
- [A1] Uses uₙ > 4.
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