Sorry if this is in the wrong forum, I think it's right but I'm not totally sure.(adsbygoogle = window.adsbygoogle || []).push({});

I'm (slowly) working my way through Roger Penrose's brilliant book Road to Reality. Recently I finished chapter four (Magical Complex Numbers) and one thing had me confused. How does he go about getting those formulae for the power series? For example, the series

1 + x^2 + x^4 + x^6 + x^8 ....

He gives the formula

(1 - x^2)^-1

How is this formula derived from the power series?

Thanks in advance :)

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# Simple question regarding formulae for power series

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