Infinite geometric series problem

AI Thread Summary
The discussion centers on determining the values of x for which the infinite geometric series 1 + (2x/3) + (2x/3)^2 + ... converges. Convergence of a geometric series occurs when the absolute value of the common ratio, in this case (2x/3), is less than 1. Participants clarify that the series converges if -1 < (2x/3) < 1, leading to the conclusion that x must be within the interval (-3/2, 3/2). A formula for the sum of a converging geometric series is also mentioned, emphasizing the importance of identifying the first term and common ratio. Understanding these concepts is crucial for solving the problem effectively.
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Homework Statement



Consider the following infinite geometric series: 1 + (2x/3) + (2x/3)^2 + (2x/3)^3 + ...

for what values of x does the series converge?

Homework Equations



i don't know what converge means, i guessed it was for what vlaues does the geometric series is infinite but i am not sure.

The Attempt at a Solution

 
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well remember that in order for a geometric series to converge all its terms should be greater than -1 and smaller than 1? do u know what to do now?
 
well, I'm going through this type of math, now there is a formula for geometric series, it is like this: (first term) / (1-r)

you always want to plug the first term in the top of the equation, in your case it looks like 1.
 
rcmango said:
well, I'm going through this type of math, now there is a formula for geometric series, it is like this: (first term) / (1-r)

you always want to plug the first term in the top of the equation, in your case it looks like 1.

Well, he is looking for something else, he just needs to find the interval of x for which the series converges.
 
thank you so much for that hint it really cleared everything! the web pages kept talking aobut limitations...i remebered now! thanks
 
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
Since ##px^9+q## is the factor, then ##x^9=\frac{-q}{p}## will be one of the roots. Let ##f(x)=27x^{18}+bx^9+70##, then: $$27\left(\frac{-q}{p}\right)^2+b\left(\frac{-q}{p}\right)+70=0$$ $$b=27 \frac{q}{p}+70 \frac{p}{q}$$ $$b=\frac{27q^2+70p^2}{pq}$$ From this expression, it looks like there is no greatest value of ##b## because increasing the value of ##p## and ##q## will also increase the value of ##b##. How to find the greatest value of ##b##? Thanks

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