Problem

Use the Ratio Test to determine if the following series converges absolutely or diverges. \[ \sum_{n=1}^{\infty} \frac{4^{n}}{n !} \]

Solution

Step 1 :We are given the series \(\sum_{n=1}^{\infty} \frac{4^{n}}{n!}\). We need to determine whether this series converges or diverges.

Step 2 :We use the Ratio Test to determine this. The Ratio Test involves taking the limit as n approaches infinity of the absolute value of the ratio of the (n+1)th term to the nth term of the series.

Step 3 :Let's calculate the ratio of the (n+1)th term to the nth term of the series: \(\frac{n!}{(n+1)!} \cdot \frac{4^{n+1}}{4^{n}}\)

Step 4 :Simplify the ratio to get \(\frac{4}{n+1}\)

Step 5 :As n approaches infinity, the ratio simplifies to 0

Step 6 :Since this value is less than 1, the series converges absolutely according to the Ratio Test.

Step 7 :Final Answer: The series converges absolutely because \(r=\boxed{0}\)

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Source: https://solvelyapp.com/problems/LFliLDYxiN/

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