Bounding a Recursive Term

Problem

In a sequence {an}\{a_n\}, a1=3a_1=3 and an+1an+λan+1+μan2=0a_{n+1}a_n+\lambda a_{n+1}+\mu a_n^2=0 for nNn\in\mathbb N^{*}.

1. If λ=0\lambda=0 and μ=2\mu=-2, find the general term of {an}\{a_n\}. 2. If λ=1k0\lambda=\dfrac 1{k_0} (where k0Nk_0\in\mathbb N^{*}, k02k_0\geqslant 2) and μ=1\mu=-1, prove that

2+13k0+1<ak0+1<2+12k0+1.2+\frac 1{3k_0+1}<a_{k_0+1}<2+\frac 1{2k_0+1}.

Answer

Solution

Difficulty9/10
TopicsMonotonicity, Recursion, sequences, Telescoping, inequality

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