Convergence of Infinite Series with Increasing Denominators

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In summary, the person was seeking help to calculate the sum of a series that did not seem to converge. However, someone informed them that the series does converge and is a well-known series. The person then asked for instructions on how to calculate the sum and was advised to look at Taylor series. They later found the answer themselves by using the Taylor expansion of e^x at 1/2.
  • #1
pixel01
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S=1/2+1/(2*4)+1/(2*4*6)...+1/(2*4*6..2n)+...

I want to calculate the sum of this series, but it seems not to converge.
Can anyone help me

Thank you.
 
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  • #2
It does converge, the sum is[tex]\sum_{n=1}^{\infty} \frac{1}{n!2^n}[/tex]

which is a well known series (what Taylor series do you know?).
 
  • #3
Thank you, yes it does converge. Could you please tell me how to calculate the sum.
I should revise some old maths books.
 
  • #4
He did tell you how to calculate the sum:
matt grime said:
which is a well known series (what Taylor series do you know?).
 
  • #5
I found it myself. The Taylor expansion of e^x at 1/2. Thanks.
 

FAQ: Convergence of Infinite Series with Increasing Denominators

Does the series converge?

The answer to this question depends on the specific series being examined. Some series converge, meaning that the sum of all terms in the series approaches a finite value as the number of terms increases. Other series diverge, meaning that the sum of all terms in the series either approaches infinity or does not approach a finite value as the number of terms increases.

How can I determine if a series converges?

There are a few different ways to test for convergence in a series. One method is to use the ratio test, which compares the absolute value of each term in the series to the term before it. If the limit of this ratio is less than 1, the series converges. Another method is the integral test, which compares the series to an integral function. If the integral converges, the series converges as well.

What is the difference between absolute and conditional convergence?

Absolute convergence occurs when the value of a series converges regardless of the order in which the terms are added. Conditional convergence, on the other hand, occurs when the value of a series depends on the order in which the terms are added. In other words, rearranging the terms of a conditionally convergent series can result in a different sum.

Can a series converge to more than one value?

No, a series can only converge to one value. If a series converges to a value, then by definition, the sum of all terms in the series approaches that specific value. If a series converges to more than one value, then it would not have a well-defined sum.

Are there any shortcuts or tricks to determine if a series converges?

While there are no shortcuts or tricks to determine if a series converges that are applicable to all series, there are some common patterns and series types that can make the process easier. For example, geometric series with a common ratio between -1 and 1 always converge. Additionally, series that involve factorial or exponential terms tend to converge, while alternating series may require additional methods such as the alternating series test.

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