How to Use Integration and Derivatives to Find the Sum of a Series

In summary, the conversation discusses using the Taylor series to find the sum of a series involving x2n-1/(2n-1). The speaker suggests substituting x2 for x and using integration and derivatives to transform the series into a familiar form. By changing the limits and using the same Taylor series, the speaker is able to find the sum as x2n+1/(2n+1).
  • #1
Dell
590
0

Σ (x2n-1)/(2n-1)
n=1

what i tried to do was take the taylor series:


Σ (xn)=1/(1-x)
n=1

so i can substitute x2 for x


Σ (x2n)=1/(1-x2)
n=1


now i need to to use some form of integration/derivative to get to my series from the taylor series,
my problem is that integral will give me x2n+1/(2n+1) , and derivative will give me 2n*x2n-1, but i need the format of the integration- a division format- but the numberss from the derivative- 2n-1 -
 
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  • #2
Hint: Change the limits to n = 0 to ∞ and (2n - 1) to (2n + 1).
 
  • #3
tell me if this is right


Σ x2n-1/(2n-1)
n=1
=

Σ x2(n+1)-1/(2(n+1)-1)
n=0
=

Σ x2n+1/(2n+1)
n=0

fx= 1/(1-x) = Σ xn
x==>x2
fx= 1/(1-x2) = Σ x2n

[tex]\int[/tex]fx=[tex]\int[/tex]1/(1-x2)=[tex]\int[/tex]Σ x2n

0.5*ln|(1+x)/(1-x)| = x2n+1/2n+1

and i can do all of this because i say n=1, and n*=0, therefore n* goes from 0-∞ and n goes from 1-∞, making n*=n+1 so i can use the same taylor series, but instead of n, i write n+1
 
  • #4
Ya looks good.
 

1. What is the formula for finding the sum of a series?

The formula for finding the sum of a series is S = a1 + a2 + a3 + ... + an, where S is the sum and a1, a2, a3, ... ,an are the individual terms of the series.

2. How do I find the sum of a series with a finite number of terms?

To find the sum of a series with a finite number of terms, you can use the formula S = (n/2)(a1 + an), where n is the number of terms and a1 and an are the first and last terms, respectively.

3. Can a series have an infinite number of terms?

Yes, a series can have an infinite number of terms. These types of series are called infinite series and require a different approach to find their sum.

4. What is the difference between a finite and an infinite series?

A finite series has a specific and fixed number of terms, while an infinite series has an unlimited number of terms. In other words, a finite series has an end point, while an infinite series continues indefinitely.

5. How do I find the sum of an infinite series?

To find the sum of an infinite series, you can use various mathematical techniques such as geometric series, telescoping series, or power series. It is important to understand the properties and behavior of the series to determine the appropriate method for finding its sum.

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