If we have the series [itex]\sum_{n=0}^{\infty} 2^{-n}x^{3n}[/itex]. We need to calculate the radius of convergence...the textbook says that, since the power of x is 3n instead of 3, we need to rewrite it in the form [itex]\sum_{n=0}^{\infty} a^{n}x^{n}[/itex]..and we say that [itex]a_{3k}=2^{-k}[/itex]. I'm not sure if I understand this...so are they setting n=3k? But we know that the power of 2 is -n, so if n=3k then doesn't the power of 2 need to be -3k?(adsbygoogle = window.adsbygoogle || []).push({});

Thanks in advance

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# A Question about Power Series

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