For this question, I'm not sure how the fact that $|a_n|<6$ effects the result of this question. I'm not really sure how to complete the proof. Here is what I have so far. Can anyone please help me out?
Consider the sequence defined by $a_{n+1} =
\sqrt{2+a_n}$ if $n ≥ 1$ and $a_1 = 1$.
Suppose that $|a_n| < 6$ for all n ∈ N. Does $\{a_n\}$ converge or diverge? Make sure to
fully prove your claim and cite appropriate theorem(s) and hypothesis conditions.
$a_2 = \sqrt{2+1} = \sqrt{3}$
$a_3 = \sqrt{2+\sqrt{3}}$
Wts there exists an M st $a_n \le M$
Choose M = 2 since the sequence eventually apporaches 2.
Base Case: $a_1 = 1 < 2$
Induction Hypothesis: Let k ∈ N be arbitrary.
Assume $a_k \le 2$
Induction Step: $a_{k+1} \to a_k$
$a_{k+1} = \sqrt{2+a_k} < \sqrt{2+2} = 2$
Therefore by induction, the sequence is bounded above
$a_n^2 - a_{n+1}^2 = a_n^2 - \sqrt{{2+a_n}}^2 = a_n^2 - a_n - 2 = (a_n-2)(a_n+1)$
$a_n^2 - a_{n+1}^2 <0$
$a_n^2 < a_{n+1}^2$
$a_n < a_{n+1}$
Therefore by the difference test, $\{a_n\}$ is strictly increasing.
Therefore by the bounded monotone convergence theorem,$\{a_n\}$ converges.
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