/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 37 Let \(\left\\{f_{n}\right\\}\) d... [FREE SOLUTION] | 91Ó°ÊÓ

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Let \(\left\\{f_{n}\right\\}\) denote the Fibonacci sequence. Prove that \(f_{n+1} f_{n}=\sum_{i=1}^{n} f_{i}^{2}\) for all \(n \geq 1\)

Short Answer

Expert verified
By induction, the property holds for all \(n \geq 1\).

Step by step solution

01

Understand the Fibonacci Sequence

The Fibonacci sequence is a series of numbers where each term is the sum of the two preceding ones. It starts with 0 and 1, so \(f_1=1\), \(f_2=1\), \(f_3=2\), \(f_4=3\), and so on.
02

State the Property to Prove

We need to prove that \( f_{n+1}f_n = \sum_{i=1}^{n} f_i^2 \). This means that the product of the \((n+1)\)-th and \(n\)-th Fibonacci number should equal the sum of the squares of all Fibonacci numbers up to \(f_n\).
03

Base Case Verification

Check the base case where \(n=1\):- Left-hand side: \(f_2f_1 = 1 \times 1 = 1\)- Right-hand side: \(\sum_{i=1}^{1} f_i^2 = f_1^2 = 1^2 = 1\)Both sides are equal, so the base case holds.
04

Inductive Hypothesis

Assume the statement is true for some \(n=k\), i.e., \(f_{k+1}f_k = \sum_{i=1}^{k} f_i^2\). This is our inductive hypothesis.
05

Inductive Step Proof

Prove the statement for \(n=k+1\):- Left-hand side: \(f_{k+2}f_{k+1} = (f_{k+1} + f_{k})f_{k+1} = f_{k+1}^2 + f_kf_{k+1}\).- Right-hand side: \(\sum_{i=1}^{k+1} f_i^2 = \sum_{i=1}^{k} f_i^2 + f_{k+1}^2\).By the inductive hypothesis, replace \(\sum_{i=1}^{k} f_i^2\) with \(f_{k+1}f_k\):\[f_{k+1}f_k + f_{k+1}^2\]Both sides simplify to the same expression showing the statement holds for \(n=k+1\).
06

Conclusion

Given the base case is true and the inductive step is also true, by mathematical induction, \(f_{n+1}f_n = \sum_{i=1}^{n} f_i^2\) holds for all \(n \geq 1\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Mathematical Induction
Mathematical induction is like a domino effect. If one domino falls, it causes the next one to fall, and the next, and so on. In mathematics, it is a technique to prove a statement for an infinite number of cases. We use it to demonstrate that a formula or an equation holds true for every integer greater than or equal to a specific starting point.

Here, the task is to prove that the product of two consecutive Fibonacci numbers equals the sum of the squares of all previous Fibonacci numbers for any positive integer. By showing the base case holds, and then that if it holds for some integer \( n \), it also holds for \( n+1 \), we cover all possible cases.

Induction involves two key steps: the base case and the inductive step, both of which must be true for the statement to be true for all numbers.
Base Case
The base case is the foundation of mathematical induction, its starting point. It involves proving that the statement holds true for the initial value, usually \( n = 1 \). Think of it as the first domino that needs to fall to start the chain reaction.

In the context of the Fibonacci sequence problem, our base case is \( n = 1 \). We calculate the product of the first two Fibonacci numbers: \( f_2f_1 = 1 \times 1 = 1 \). Next, we need to check if this is indeed equal to the sum of the squares of Fibonacci numbers up to \( f_1 \), which is \( f_1^2 = 1^2 = 1 \).

Since both the left-hand and right-hand sides of the equation are equal, our base case is satisfied, paving the way to tackle the inductive step.
Inductive Step
The inductive step is where we make a leap of faith based on the inductive hypothesis. We assume the statement holds true for a particular number \( n = k \), and then prove it for \( n = k+1 \). This is akin to showing that if one domino falls, the next one must fall too.

In the Fibonacci sequence proof, our inductive hypothesis assumes \( f_{k+1}f_k = \sum_{i=1}^{k} f_i^2 \). Next, we demonstrate it holds for \( k+1 \): The left-hand side becomes \( f_{k+2}f_{k+1} = (f_{k+1} + f_k)f_{k+1} = f_{k+1}^2 + f_kf_{k+1} \). For the right-hand side, the sum extends by adding \( f_{k+1}^2 \) to the existing sum, \( \sum_{i=1}^{k} f_i^2 + f_{k+1}^2 \).

By substituting the inductive hypothesis into this equation, both sides simplify to the same expression, thus proving our statement for \( n = k+1 \). This confirms that the statement is true for any positive integer \( n \).
Sum of Squares
The sum of squares is a recurring mathematical theme where we add together squares of numbers. In our case, it focuses on the squares of Fibonacci numbers.

The equation we want to establish is that the product of consecutive Fibonacci numbers equals the sum of the squares of all previous Fibonacci numbers. Let's break it down: for any \( n \), the sum \( \sum_{i=1}^{n} f_i^2 \) involves squaring each Fibonacci number from the first to the \( n \)-th. This becomes the right-hand side of our equation.

Understanding the sum of squares helps us verify the equality with the product on the left-hand side during each step of our inductive proof. It's these squares that ultimately match the product of Fibonacci terms, beautifully illustrating the relationship within this numerical sequence.

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Most popular questions from this chapter

Consider the sequence defined by \(a_{1}=1, a_{n+1}=\) \((n+1)^{2}-a_{n}\) for \(n \geq 1 .\) Find the first six terms. Guess a general formula for \(a_{n}\) and prove that your answer is correct.

Given that each sum below is the sum of part of an arithmetic or geometric sequence, find each sum. (a) \([\mathrm{BB}] 75+71+67+63+\cdots+(-61)\) (b) \(75+15+3+\frac{3}{5}+\cdots+\frac{3}{5^{7}}\) (c) \(-52-41-30-19+\cdots+949\) (d) \(1-\frac{1}{2}+\frac{1}{4}-\frac{1}{8}+\cdots+\frac{1}{2^{60}}\) (e) \(2+6+18+54+\cdots+354,294\)

Express the generating function of each of the following sequences as a polynomial or as the quotient of polynomials. (a) \([\mathrm{BB}] 1,2,5,0,0, \ldots\) (b) \(0,1,4,1,0,0, \ldots\) (c) \(1,2,4,8,16, \ldots\) (d) I, \(-1,1,-1, \ldots\) (e) \(3,3,3, \ldots\) (f) \([\mathrm{BB}] 1,0,1,0, \ldots\) (g) \(1,-2,3,-4, \ldots\)

It is tempting to think that if a statement involving the natural number \(n\) is true for many consecutive values of \(n\), it must be true for all \(n .\) In this connection, the following example due to Euler is illustrative. Let \(f(n)=n^{2}+n+41\). (a) Convince yourself (perhaps with a computer algebra package like Maple or Mathematica) that \(f(n)\) is prime for \(n=1,2,3, \ldots 39\) but that \(f(40)\) is not prime. (b) Show that for any \(n\) of the form \(n=k^{2}+40, f(n)\) is not prime.

Define a sequence \(\left\\{a_{n}\right\\}\) recursively as follows: \(a_{0}=0, \quad\) and for \(n>0, \quad a_{n}=a_{\lfloor n / 5\rfloor}+a_{[3 n / 5\rfloor}+n\) Prove that \(a_{n} \leq 20 n\) for all \(n \geq 0\). (Recall that \(\lfloor x\rfloor\) denotes the floor of the real number \(x\). See paragraph 3.1.6.)

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