Fibonacci numbers @ HMMT

by t0rajir0u, Feb 21, 2009, 10:11 PM

Today I gave a talk at the Harvard-MIT Math Tournament as a mini-event on the Fibonacci numbers. The slides are available here (~1 MB).

The focus of the talk was the material from this post and this post and, to a lesser extent, this post. Briefly, there are three ways to think about the proof of Binet's formula:

1. The space of sequences satisfying $ F_{n+2} = F_{n+1} + F_n$ is ia vector space of dimension $ 2$, and there exists a basis consisting of the two geometric sequences $ \phi^n, \varphi^n$.

2. The generating function $ \sum_{n \ge 0} F_n x^n$ has a partial fraction decomposition.

3. The powers of the matrix $ \left[ \begin{array}{cc} 1 & 1 \\ 1 & 0 \end{array} \right]$ describe the Fibonacci numbers and this matrix is diagonalizable.

As I discussed in some of the posts above, these proofs are essentially the same (although it is the third that leads into the material from this post, which I unfortunately didn't have enough time to cover); each is about relating geometric series to the eigenvectors of a shift operator. See the posts above or the slides for details.

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I was there good job

by Bijection, Feb 22, 2009, 10:18 PM

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Me too. XD

by Zhero, Feb 22, 2009, 11:02 PM

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[please refer to the above posts]

by mz94, Feb 23, 2009, 2:06 AM

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you do it simply by difference equations and it does not need those complication!

by Anonymous, Feb 28, 2009, 2:51 AM

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The purpose of providing both simple and sophisticated solutions is to unify them and use them to point out more general principles; I don't talk about Binet's formula solely for the sake of Binet's formula.

by t0rajir0u, Feb 28, 2009, 11:08 PM

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What's the solution to the problem you posted in the beginning of the lecture?

by nittanylion, Apr 1, 2009, 10:42 PM

Various mathematical thoughts, ranging from problem-solving techniques to attempts to tie together related concepts.

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