Powerseries of a natural logarithm

In summary, the conversation discusses how to prove the equation \frac{1}{x} \ln \frac{x+1}{x-1} = \sum_0^\infty \frac{2x^{2n}}{2n+1} by using the relation \frac{1}{1+x} = \frac{d}{dx}\ln (1+x) and expanding as a geometric series. It is initially thought that this method will not work due to an alternating series, but it is later realized that subtracting the resulting series will lead to a solution. The conversation ends with a thank you for the helpful hint about using the property \log\left(\frac{a}{b}\right) = \log
  • #1
center o bass
560
2

Homework Statement


Show that

[tex]\frac{1}{x} \ln \frac{x+1}{x-1} = \sum_0^\infty \frac{2x^{2n}}{2n+1}[/tex].


2. The attempt at a solution
I tried to use the relation

[tex]\frac{1}{1+x} = \frac{d}{dx}\ln (1+x)[/tex]

and expand as a geometric series, but this did not lead anywhere since I then ended up with an alternating series.

Anyone got any ideas of where to start?
 
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  • #2
HINT:

[tex]\log\left(\frac{a}{b}\right) = \log a - \log b[/tex]
 
  • #3
Yes, so I could subtract the two resulting series... and I see now that it will actually lead trough. Ofcourse I knew about the property, but I did not see how it would get rid of the 'alternation'. However I do see that now because of the cancellation of terms.

Thank you!
 

1. What is a power series of a natural logarithm?

A power series of a natural logarithm is an infinite series representation of the natural logarithm function. It is expressed as the sum of terms with increasing powers of a variable, typically x, multiplied by coefficients.

2. How is the power series of a natural logarithm derived?

The power series of a natural logarithm is derived using the Maclaurin series, which is a special case of the Taylor series. The Maclaurin series is used to approximate a function with an infinite polynomial series centered at x=0.

3. What is the convergence radius of the power series of a natural logarithm?

The convergence radius of the power series of a natural logarithm is infinite, meaning it converges for all values of x. However, the series may not converge for values of x that are equal to or close to 0, due to the singularity of the natural logarithm function at that point.

4. How is the power series of a natural logarithm used in mathematics?

The power series of a natural logarithm is used in mathematics to approximate the value of the natural logarithm function at a given point, especially when the value is not easily computable. It is also used in calculus and differential equations to solve problems involving the natural logarithm function.

5. Can the power series of a natural logarithm be generalized to other logarithmic functions?

Yes, the power series method can be used to find infinite series representations for other logarithmic functions, such as the base 10 logarithm or the natural logarithm of a complex number. However, the specific coefficients and convergence radius will vary for each function.

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