Lucas Numbers and Generating Functions

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Homework Help Overview

The discussion revolves around the Lucas numbers and their relationship to generating functions, particularly through the lens of Fibonacci numbers. The original poster presents a problem involving the Lucas sequence and seeks to derive an explicit formula using generating functions.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants explore the use of generating functions to relate Lucas numbers to Fibonacci numbers. The original poster attempts to establish a connection through summations involving Fibonacci numbers, while others suggest direct relationships and methods for solving the generating function.

Discussion Status

There is an ongoing exploration of how to derive the Lucas numbers using Fibonacci numbers, with some participants providing insights into the relationships and methods to apply. The conversation reflects a mix of interpretations and approaches without a definitive consensus yet.

Contextual Notes

The original poster notes a requirement to specifically use Fibonacci numbers in their approach to generating the Lucas numbers, which influences the direction of the discussion.

Johnny Numbers
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Here is my problem and my attempt at the answer. Any help or advice is highly appreciated.
Problem
With the famous sequence of Lucas numbers 1, 3, 4, 7, 11, 18... (Where each number is the sum of the last two and the first two are defined as 1 and 3.) use generating functions to find an explicit formula for the Lucas function.
Attempted Solution
We have
\sum_{j=1}^{n}F_jx^j
where Fj denotes the jth Fibonacci number and n is going to infinity. Then we add that to
\sum_{j=-1}^{n}F_jx^j^+^2
Where F-1 = -1 and F0 = 0

And that should get us a function of Lucas numbers right?:confused:
 
Last edited:
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The Lucas numbers satisfy the relation

L_{n+1} = L_n + L_{n-1}

Just set L_n = a^n and solve for a. Your generating function will be a linear combination of the two solutions. Apply your initial conditions ( L_1 and L_2) to determine the two arbitrary constants and you're done! :)
 
I should've been more specific, but we have to use the Fibonacci numbers to generate the Lucas numbers in this manner.

EDIT: I changed it up a little bit as well.
 
Last edited:
In that case, it should be apparent that L_n = F_{n+1} + F_{n-1}
 
Ok so I believe that matches what I was intending on getting at. Thank you again.
 

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