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Sia

钰皓's Question
Math
Posted 2 months ago

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Given un=1(1+n)nu_{n}=\frac{1}{(1+\sqrt{n})^{n}} defined for nNn \in \mathbb{N}, what is the nature of un\sum u_{n} ?

Converging

Diverging
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Answer from Sia
Posted 2 months ago
Solution by Steps
step 2
We can rewrite un u_n as un=(1+n)n u_n = (1+\sqrt{n})^{-n} . Taking the limit, we have limnun=limn(1+n)n \lim_{n \to \infty} u_n = \lim_{n \to \infty} (1+\sqrt{n})^{-n}
step 3
As n n approaches infinity, n \sqrt{n} dominates, and we can approximate (1+n)n (1+\sqrt{n})^{-n} as (n)n=nn/2 \left(\sqrt{n}\right)^{-n} = n^{-n/2} . Thus, limnun=0 \lim_{n \to \infty} u_n = 0
step 4
Since un u_n approaches 0, we can apply the ratio test or comparison test to determine the nature of the series. The terms un u_n decrease rapidly, indicating convergence
step 5
Therefore, the series un \sum u_n converges
A
Key Concept
Convergence of Series
Explanation
A series converges if the terms approach zero and decrease sufficiently fast, which is the case for un u_n .

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