>Prove that Fib(n) is the closest integer to (φ^n)/√5, where φ = (1 + √5)/2.
Hint: Let ψ = (1 - √5)/2. Use induction and the definition of the Fibonacci numbers (see section 1.2.2) to prove that Fib(n) = (φ^n - ψ^n ) / √5.
What the fuck is this shit?!?!? How am I supposed to know how to do this? I didn't even know what the golden ratio actually was until I looked it up while researching the problem.
How can I be expected to inductively prove something when I just finished the very first chapter of the book?
I know that phi (φ) represents a number that is the result of (1 + √5)/2, by way of using that algebraic formula.
The other possible number, (1 - √5)/2, is represented by psi (ψ).
I also know the ratio, fib(n+1) / fib(n) approaches the value of φ as the fibonnaci sequence grows (as n increments).
How can I show that by placing n as the exponent of φ, the value of (φ^n)/√5 will be the fib (n)?
From wikipedia....
>any power of φ is equal to the sum of the two immediately preceding powers
Which is just another way of connecting the Fibonacci sequence and the golden ratio.
Other websites created base cases by using the equations in terms of psi and phi to calculate Fib (1) and Fib (0),
What can I do with this information? I know that the problem makes use of something called Binet's formula (or something similar).
...does anyone know SICP?
I'd love a hint, pls
there are probably other anons who will be able to help you more, but this is how i think you would do it
proof by induction should be fairly straightforward with the hint they gave you. if not, various proofs for the closed form of fibonacci numbers are probably widely available online. then since ψ^n = (-1/φ)^n, you could prove |ψ^n/sqrt(5)| < 1/2 for all n >= 0, which i found here
https://en.wikipedia.org/wiki/Fibonacci_number#Computation_by_rounding
which would complete the proof
>>58332447
Thanks, sorry for the freakout post. I'm trying to go solo and it's my first language.
How did you come upon this problem, OP?