# Thread: Simplify this infinite convergent sum.

1. ## Simplify this infinite convergent sum.

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Simplify the infinite convergent sum as much as possible in terms of $\phi$:

$\dfrac{1}{\phi^1} + \dfrac{1}{\phi^2} + \dfrac{1}{\phi^3} \ + \ ...$

where $\phi$ equals $\dfrac{\sqrt{5} + 1}{2}$.

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Source:

The Call Of The Primes: Surprising Patterns, Peculiar Puzzles, and Other Marvels of Mathematics

by Owen O'Shea

pages 123, 125-126

2. ## Re: Simplify this infinite convergent sum.

This is a geometric series:

$\sum_{n\ge 1}\left(\dfrac{1}{\phi}\right)^n = \left[\sum_{n\ge 0}\left(\dfrac{1}{\phi}\right)^n\right]-1=\dfrac{1}{1-\dfrac{1}{\phi}}-1 = \dfrac{1}{\phi-1}=\phi$