Power series and finding radius of convergence

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The discussion focuses on finding the radius and interval of convergence for the series ∑(x^n/n!). The Ratio Test is applied, leading to the limit of |x|/(n+1) as n approaches infinity, which converges to 0 for any x. This indicates that the series converges for all real numbers, resulting in an infinite radius of convergence. The confusion arises regarding handling an extra N term during calculations, but it is clarified that it does not affect the outcome. Ultimately, the series converges for every chosen x, confirming that the radius of convergence is infinite.
cowmoo32
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Homework Statement


"Find the radius of convergence and interval of convergence of the series"
\sum_{n=0}^\infty \frac{x^n}{n!}

Homework Equations



Ratio Test

The Attempt at a Solution



\lim{\substack{n\rightarrow \infty}} |x/n+1|
(I can't seem to get the |x/n+1| to move up where it should be)

Here's what I don't understand. What do I do if I have an N left over when I get this far?
 
Last edited:
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After using ration test i get

lim x^(n+1)/(n+1)! *(n)/(x^n)! = (x)/(n+1)

ration of convergence is then n-> infinite |x|/n+1 -> 0

so for every chosen x you will get convergence Then R=infinite

Garret
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Imagination is more important than knowlegde - A.Einstein
 
Thanks man. I just got off the phone with my friend and he told me the same thing. I'm not sure waht I was thinking...it's been a long day.
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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