Logical Algebra (Problem 2 - Version 2)

Algebra Level 2

The Lucas numbers are related to the Fibonnaci numbers. Their relation identities are listed in the picture below: Also, a closed-form expression of the Lucas numbers is given below: And finally, the closed-form expression of the Lucas numbers being combined with the Binet formula to create a formula for [ ϕ ] n [{\displaystyle \phi }]^n : So, my question to you is this: how many of the Fibonnaci - Lucas numbers relation identities are equivalent to each other? (-1 if none, >= 1 if any of the identities are equivalent to each other.)

Bonus: Prove that the addition of the first 7 Lucas polynomials is equivalent to: x 3 + ( x + 6 ) ( x + 1 ) x^3 + (x + 6) (x + 1) + + 14 x 2 + 9 x + 8 x 3 \frac{14x^2 + 9x + 8}{x^3} . Here are the first seven Lucas polynomials: 2 2 , x + 2 x + 2 , x 2 + 2 x^2 + 2 , x 3 + 3 x x^3 + 3x , x 4 + 4 x 2 + 2 x^4 + 4x^2 + 2 , x 5 + 5 x 3 + 5 x x^5 + 5x^3 + 5x and x 6 + 6 x 4 + 9 x 2 + 2 x^6 + 6x^4 + 9x^2 + 2 (this is Logical Algebra (Problem 3) - how to get there explained in Logical Algebra (Problem 3).)

Bonus 2: Prove that F 3 ( x ) + 2 F 2 ( x ) = ( x + 1 ) 2 F_3(x) + 2F_2(x) = (x + 1) ^2 where F n ( x ) F_n(x) is a Fibonnaci polynomial.

Bonus 3: Prove that L 1 ( x ) + F 2 ( x ) + L 0 ( x ) = 2 ( x + 1 ) L_1(x) + F_2(x) + L_0(x) = 2 (x + 1) where F n ( x ) F_n(x) is a Fibonnaci polynomial and L n ( x ) L_n(x) is a Lucas polynomial.

Challenge: n ( n + 1 ) 2 \frac{n(n + 1)}{2} = L n ( 19 ) L_n(19) where L n ( 19 ) L_n(19) is the 19th Lucas number. Using L n = [ ϕ n ] L_n = [{\displaystyle \phi^n}] , find the 19th Lucas number and hence prove using n ( n + 1 ) 2 \frac{n(n + 1)}{2} that the 19th Lucas number is one of only three triangular numbers in the Lucas series (or the Lucas number sequence.)

Place your answers to Bonuses 2, 3 and the Challenge in the Discussion Section.


The answer is -1.

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1 solution

Since the first four aren't equivalent to each other, the first four isn't considered. As for the last two, the second has a different right-hand side to the first as well as one sign change, therefore it's -1.

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