What Is the Significance of the Math Series X + 1 (1/x + 1/x^2 + 1/x^3 ...)?

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The series X + 1 (1/x + 1/x^2 + 1/x^3 ...) involves a geometric progression within the parentheses. This geometric series can be summed to yield 1/(x-1), given that the absolute value of x is greater than 1. The convergence condition for the series is that |1/x| must be less than 1. Understanding this series is significant for various mathematical applications, particularly in projects requiring convergence analysis. This series is valuable for anyone exploring mathematical concepts related to infinite series and their practical uses.
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I have no math training beyond high school 45 years ago, and I don’t remember much of it. However I am doing a project, and I find the series below is quite valuable. But I do not know what it is or what it is called. It is like this:

X + 1 (1/x + 1/x^2 + 1/x^3 . . . ).

It comes ever closer to a value which is very significant in what I am doing. I wonder if someone can tell me what this is called, and what it can be used for.
 
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Well what is in the brackets is a geometric progrssion
 
Yes, the part in parentheses is a geometric series that can be summed (provided the absolute value of x is bigger than 1):

1/x + 1/x^2 + 1/x^3 + ... = 1/(x-1)
 
Thank you!
 
Avodyne said:
Yes, the part in parentheses is a geometric series that can be summed (provided the absolute value of x is bigger than 1):

1/x + 1/x^2 + 1/x^3 + ... = 1/(x-1)

For that sum to converge,

|1/x|<1
 
I tried to combine those 2 formulas but it didn't work. I tried using another case where there are 2 red balls and 2 blue balls only so when combining the formula I got ##\frac{(4-1)!}{2!2!}=\frac{3}{2}## which does not make sense. Is there any formula to calculate cyclic permutation of identical objects or I have to do it by listing all the possibilities? Thanks
Essentially I just have this problem that I'm stuck on, on a sheet about complex numbers: Show that, for ##|r|<1,## $$1+r\cos(x)+r^2\cos(2x)+r^3\cos(3x)...=\frac{1-r\cos(x)}{1-2r\cos(x)+r^2}$$ My first thought was to express it as a geometric series, where the real part of the sum of the series would be the series you see above: $$1+re^{ix}+r^2e^{2ix}+r^3e^{3ix}...$$ The sum of this series is just: $$\frac{(re^{ix})^n-1}{re^{ix} - 1}$$ I'm having some trouble trying to figure out what to...
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