/*! 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 15 While the above proof does not w... [FREE SOLUTION] | 91Ó°ÊÓ

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While the above proof does not work (it better not since the statement it is trying to prove is false!) we can prove something similar. Prove that there is a strictly increasing sequence \(a_{1}, a_{2}, a_{3}, \ldots\) of numbers (not necessarily integers) such that \(a_{n}<100\) for all \(n \in \mathbb{N}\). (By strictly increasing we mean \(a_{n}

Short Answer

Expert verified
The sequence defined by \(a_{1}=0\) and \(a_{n+1} = a_{n} + \frac{1}{n+1}\) is a strictly increasing sequence where each term is less than 100 for all natural numbers \(n\).

Step by step solution

01

Understanding the concept

The exercise requires us to construct a strictly increasing sequence of numbers where each term is less than 100. This means we need to choose an initial number and a way to generate the next terms such that each term is greater than the previous one, but still less than 100.
02

Choosing the initial term

Pick an arbitrary starting number for the sequence that is less than 100. For the sake of simplicity, let's choose the initial term to be 0, denoted by \(a_{1}=0\).
03

Constructing the sequence

Define a rule to generate the next term in the sequence. A straightforward way is to add a number that gets smaller as \(n\) increases but never reaches 0, to ensure that the sequence does not exceed 100 and is strictly increasing. For instance, we can use the reciprocal of \(n\), which is always positive and decreasing as \(n\) increases. The sequence is then defined by \(a_{n+1} = a_{n} + \frac{1}{n+1}\), where \(n \in \mathbb{N}, n \geq 1\).
04

Verifying the condition \(a_{n}

We need to check that as \(n\) increases indefinitely, \(a_{n}\) remains below 100. The series \(\sum_{n=1}^{\infty} \frac{1}{n}\) diverges, meaning it grows without bound; however, for any finite \(n\), the sum \(\sum_{n=1}^{k} \frac{1}{n}\) for some finite \(k\), is always less than some finite upper bound. We can use the harmonic series' property that it grows very slowly to ensure that our sequence will grow slowly enough to always be less than 100 for all finite \(n\).
05

Conclusion

Thus, we have constructed the sequence \(a_{1}, a_{2}, a_{3}, \ldots\), with \(a_{1}=0\) and \(a_{n+1} = a_{n} + \frac{1}{n+1}\). This sequence satisfies all the given conditions: it is strictly increasing, as every term \(a_{n+1}\) is greater than the previous term \(a_{n}\), and each term is less than 100 for all natural numbers \(n\).

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Key Concepts

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

Discrete Mathematics
Discrete mathematics is an area of study focused on mathematical structures that are fundamentally discrete rather than continuous. This means that the values dealt within discrete mathematics do not vary smoothly, but have distinct, separated values. In the context of our exercise, the sequence of numbers is an example of such a discrete system. Each number in the sequence is distinct from the next, related through a specific formula or property, reflecting the stepwise nature of discrete phenomena. Discrete mathematics encompasses a wide range of topics, including set theory, combinatorics, graph theory, and logic, all of which provide foundational tools for computer science and algorithms.

Understanding discrete mathematics involves mastering the art of creating and manipulating discrete elements, such as sequences or sets, to solve problems. In the context of increasing sequences, it embodies the idea of crafting a progression of numbers, each following a pattern or rule, which is precisely what the exercise requires us to construct.
Natural Numbers
The concept of natural numbers is instrumental in our understanding of sequences and series. The natural numbers, commonly denoted by \(\mathbb{N}\), are the set of numbers used for counting and ordering. They are the numbers \(1, 2, 3, \ldots\) and so on ad infinitum. A key characteristic of natural numbers is that they are discrete, meaning there is a well-defined next number (successor), but there is no number between any two consecutive natural numbers.

For the exercise in question, the natural numbers serve as the indexing set for the sequence. The indexes \(n\) which signify the position of terms within the sequence \(a_n\), are themselves natural numbers. This is why it's important to understand how to construct sequences indexed by natural numbers and the properties that arise from doing so, such as the assurance of being able to continually generate discrete, new terms that maintain the strictly increasing nature of the sequence.
Harmonic Series
The harmonic series is a famous infinite series, which is defined as the sum of the reciprocals of the natural numbers. Mathematically, it is represented as \(\sum_{n=1}^{\infty} \frac{1}{n}\). One interesting property of the harmonic series is that it diverges, meaning it increases without bound as more terms are added. However, the harmonic series grows very slowly, which becomes highly relevant in our exercise when designing a sequence that grows but always remains below a certain limit, like 100.

In constructing our strictly increasing sequence, we've essentially tapped into the nature of the harmonic series by adding decreasing fractions to each consecutive term. These fractions are tiny enough to ensure our sequence doesn't surpass our ceiling of 100. The harmonic series serves as a conceptual anchor to understand how a sequence can keep growing indefinitely in a controlled manner without limit, yet still remain finite when looking at any specific term in the series.
Proof Construction
Proof construction is a fundamental concept in mathematics that involves formulating arguments to establish the truth of mathematical statements. Proofs can use direct methods, contradiction, induction among others, and aim to ensure that conclusions follow logically and incontrovertibly from premises.

In the context of our exercise, we have constructed a proof by demonstrating the existence of a strictly increasing sequence that remains below 100. This was done by specifying a clear starting point and a rule for progression, then verifying that the conditions hold true. Proof construction in this case was not about showing that a number will eventually exceed 100, but rather that it is possible to approach it indefinitely while remaining strictly increasing and below this threshold. It showcases how mathematical reasoning is employed to offer insight and certainty in problem-solving.

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Most popular questions from this chapter

Find the closed formula for each of the following sequences by relating them to a well known sequence. Assume the first term given is \(a_{1}\). (a) \(2,5,10,17,26, \ldots\) (b) \(0,2,5,9,14,20, \ldots\) (c) \(8,12,17,23,30, \ldots\) (d) \(1,5,23,119,719, \ldots\)

Starting with any rectangle, we can create a new, larger rectangle by attaching a square to the longer side. For example, if we start with a \(2 \times 5\) rectangle, we would glue on a \(5 \times 5\) square, forming a \(5 \times 7\) rectangle: The next rectangle would be formed by attaching a \(7 \times 7\) square to the top or bottom of the \(5 \times 7\) rectangle. (a) Create a sequence of rectangles using this rule starting with a \(1 \times 2\) rectangle. Then write out the sequence of perimeters for the rectangles (the first term of the sequence would be \(6,\) since the perimeter of a \(1 \times 2\) rectangle is 6 - the next term would be 10 ). (b) Repeat the above part this time starting with a \(1 \times 3\) rectangle. (c) Find recursive formulas for each of the sequences of perimeters you found in parts (a) and (b). Don't forget to give the initial conditions as well. (d) Are the sequences arithmetic? Geometric? If not, are they close to being either of these (i.e., are the differences or ratios almost constant)? Explain.

The in song The Twelve Days of Christmas, my true love gave to me first 1 gift, then 2 gifts and 1 gift, then 3 gifts, 2 gifts and 1 gift, and so on. How many gifts did my true love give me all together during the twelve days?

Prove that every positive integer is either a power of \(2,\) or can be written as the sum of distinct powers of 2 .

Make up sequences that have (a) \(3,3,3,3, \ldots\) as its second differences. (b) \(1,2,3,4,5, \ldots\) as its third differences. (c) \(1,2,4,8,16, \ldots\) as its 100 th differences.

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