phi vs. Phi - a Coincidence?Date: 10/16/2001 at 14:10:08 From: S. Cotton Subject: phi versus "golden ratio" Ancient and modern architecture reflect the 'golden ratio' (1.618 length to width) and this number is remarkably close to phi (.618...) seen in nature for leaf dispersions, etc. Is this just a coincidence? Thanks for your reply. S. Cotton Date: 10/16/2001 at 17:00:15 From: Doctor Peterson Subject: Re: phi versus "golden ratio" It's more than just coincidence: the golden ratio (as you define it) is phi's twin, "Phi," where Phi = (sqrt(5) + 1)/2 = 1.618... phi = (sqrt(5) - 1)/2 = 0.618... Phi = 1/phi Phi = 1 + phi The latter facts together give the definition of the golden ratio: x = 1/x + 1 This equation (equivalent to x^2 - x - 1 = 0) is satisfied by both Phi and -phi, which therefore can be called the _golden ratios_. Since they are reciprocals, either could just as well be given that name. Together, these are used in the formula for the Fibonacci sequence: F[n] = (Phi^n - (-phi)^n) / sqrt(5) See Ron Knott's page for details: The Golden section ratio: Phi http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/phi.html - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994- The Math Forum at NCTM. All rights reserved.
http://mathforum.org/dr.math/