Real Numbers: Integers and Rational Numbers

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Questions and Answers

Within the framework of Dedekind cuts, a real number is defined as a partition of ______ into two non-empty subsets, $A$ and $B$, such that every element of $A$ is less than every element of $B$, and $A$ contains no greatest element.

rationals

In the context of p-adic numbers, the completion of the rational numbers with respect to the p-adic metric yields a field in which the ultrametric inequality holds: $d(x, z) \leq \max(d(x, y), d(y, z))$. This field is denoted as ______.

$Q_p$

Consider the algebraic closure of the field of rational numbers, denoted as $\overline{\mathbb{Q}}$. The elements of this field, which are roots of non-zero polynomial equations with rational coefficients, are known as ______ numbers.

algebraic

Liouville numbers are defined as real numbers $x$ for which, for every positive integer $n$, there exist integers $p$ and $q$ with $q > 1$ such that $|x - \frac{p}{q}| < \frac{1}{q^n}$. These numbers are transcendental, meaning they are not ______.

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The Riemann zeta function, defined as $\zeta(s) = \sum_{n=1}^{\infty} \frac{1}{n^s}$ for complex numbers $s$ with real part greater than 1, has a deep connection to prime numbers. The values of $s$ for which $\zeta(s) = 0$ are known as its non-trivial ______.

<p>zeros</p> Signup and view all the answers

In the context of cardinality, the set of real numbers is uncountably infinite, a consequence of Cantor's diagonalization argument. This implies that the cardinality of the real numbers is strictly greater than that of the ______.

<p>integers</p> Signup and view all the answers

The field of Laurent series, denoted as $\mathbb{C}((t))$, consists of formal expressions of the form $\sum_{n=k}^{\infty} a_n t^n$, where $k$ is an integer and the coefficients $a_n$ are complex numbers. This field extends the notion of power series and is used in complex analysis to study functions with ______.

<p>poles</p> Signup and view all the answers

Within the surreal numbers, constructed using the simplest possible inductive definition, every real number has a corresponding representation. However, the surreal numbers encompass much more, including infinitesimals and infinite numbers of various ______.

<p>sizes</p> Signup and view all the answers

The Minkowski question mark function, denoted as $?(x)$, is a singular function that maps rational numbers in $[0, 1]$ to dyadic rationals in $[0, 1]$. It is continuous and strictly increasing, but its derivative is zero almost ______.

<p>everywhere</p> Signup and view all the answers

The Farey sequence of order $n$, denoted as $F_n$, is the sequence of completely reduced fractions between 0 and 1 which have a denominator less than or equal to $n$, arranged in increasing order. These sequences are intimately connected to the distribution of rational numbers and Diophantine ______.

<p>approximation</p> Signup and view all the answers

In the context of continued fractions, every irrational number has a unique representation as an infinite continued fraction. The convergents of this continued fraction provide the best rational ______ of the irrational number.

<p>approximations</p> Signup and view all the answers

Within the realm of non-standard analysis, hyperreal numbers extend the real numbers by including infinitesimals and infinitely large numbers. These numbers are constructed using ultrafilters and allow for a rigorous treatment of calculus using ______.

<p>infinitesimals</p> Signup and view all the answers

The Grothendieck group of the natural numbers $\mathbb{N}$ under addition is isomorphic to the integers $\mathbb{Z}$. This construction formalizes the process of introducing additive inverses to a set, effectively creating both positive and ______ whole numbers.

<p>negative</p> Signup and view all the answers

The field of formal power series over a field $K$, denoted as $K[[x]]$, consists of infinite series of the form $\sum_{n=0}^{\infty} a_n x^n$, where the coefficients $a_n$ belong to $K$. Unlike polynomials, these series can have infinitely many non-zero ______.

<p>terms</p> Signup and view all the answers

In the context of algebraic number theory, the ring of integers of a number field $K$ is the integral closure of $\mathbb{Z}$ in $K$. These are the elements of $K$ that are roots of monic polynomials with ______ coefficients.

<p>integer</p> Signup and view all the answers

The Euler-Mascheroni constant, denoted by $\gamma$, is defined as the limiting difference between the harmonic series and the natural logarithm. It appears in various analytical contexts, yet it remains unknown whether $\gamma$ is rational or ______.

<p>irrational</p> Signup and view all the answers

Consider the set of all possible finite strings of digits. When equipped with a suitable metric, this set forms a complete ultrametric space. Functions that map integers to elements of this space can be used to study the properties of Integer ______.

<p>Sequences</p> Signup and view all the answers

In the context of topological groups, the p-adic integers form a compact, Hausdorff topological ring denoted by $\mathbb{Z}_p$. This means they are complete with respect to the p-adic metric and every open cover has a finite ______.

<p>subcover</p> Signup and view all the answers

Consider the Cantor set, constructed by repeatedly removing the open middle third from a closed interval. The resulting set is uncountable and has Lebesgue measure zero, yet it contains no ______.

<p>intervals</p> Signup and view all the answers

In the setting of Diophantine approximation, Roth's theorem states that if $\alpha$ is an algebraic irrational number, then for any $\epsilon > 0$, there are only finitely many rational numbers $\frac{p}{q}$ such that $|\alpha - \frac{p}{q}| < \frac{1}{q^{2+\epsilon}}$. This places a limit on how well algebraic irrationals can be approximated by ______.

<p>rationals</p> Signup and view all the answers

The Kronecker-Weber theorem states that every finite abelian extension of the rational numbers is contained in a cyclotomic field, which is a field obtained by adjoining a root of unity to $\mathbb{Q}$. This means every such extension can be generated by roots of ______.

<p>unity</p> Signup and view all the answers

The Gelfond-Schneider theorem states that if $a$ and $b$ are algebraic numbers with $a \neq 0, 1$ and $b$ irrational, then $a^b$ is transcendental. As a consequence, numbers like $2^{\sqrt{2}}$ and $e^\pi$ are known to be ______.

<p>transcendental</p> Signup and view all the answers

In the context of measure theory, the set of rational numbers has Lebesgue measure zero. This implies that, in a probabilistic sense, if you were to randomly pick a real number from a finite interval, the probability of picking a rational number is ______.

<p>zero</p> Signup and view all the answers

Consider the Thue-Siegel-Roth theorem which asserts that for any algebraic irrational number $\alpha$, and for any $\epsilon > 0$, the inequality $|\alpha - p/q| < 1/q^{2+\epsilon}$ has only finitely many solutions amongst integers $p$ and $q$. The exponent 2 in the theorem is sharp, relating closely to ______.

<p>Liouville numbers</p> Signup and view all the answers

The integer sequence A000142 in the OEIS refers to n!, which is also called the ______ numbers.

<p>Factorial</p> Signup and view all the answers

Flashcards

Real Numbers

All numbers that can be represented on a number line, including both rational and irrational numbers.

Integers

Whole numbers (positive, negative, or zero) without fractions or decimals.

Rational Numbers

Numbers that can be written as a fraction p/q, where p and q are integers and q is not zero.

Irrational Numbers

Numbers that cannot be expressed as a fraction p/q, having non-terminating and non-repeating decimal representations.

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What does the symbol 'Z' represent?

The set of whole numbers, including negative, positive, and zero.

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What does the symbol 'Q' represent?

The set of numbers expressible as a fraction p/q, where p and q are integers and q ≠ 0.

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What does the symbol 'R' represent?

The set that encompasses both rational and irrational numbers, visualized on a number line.

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What makes √2 irrational?

A number that cannot be written as a simple fraction; its decimal goes on forever.

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What is the decimal representation of irrational numbers?

The name given to numbers which decimal representation is non-terminating and non-repeating.

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What is π?

A number that is a constant representing the ratio of a circle's circumference to its diameter.

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Study Notes

  • Real numbers encompass all numbers that can be represented on a number line.

Integers

  • Integers are whole numbers, which can be positive, negative, or zero.
  • They do not include fractions, decimals, or any non-whole number components.
  • Examples of integers: -3, -2, -1, 0, 1, 2, 3.
  • The set of integers is typically denoted by the symbol 'Z'.
  • Integers are fundamental in arithmetic and number theory.
  • They can be used for counting discrete objects.

Rational Numbers

  • Rational numbers can be expressed as a fraction p/q, where both p and q are integers, and q is not zero.
  • The term 'rational' comes from 'ratio', highlighting their fractional nature.
  • Examples of rational numbers: 1/2, -3/4, 5 (since 5 can be written as 5/1), 0.75 (which is 3/4).
  • Decimal representations of rational numbers either terminate (e.g., 0.25) or repeat in a pattern (e.g., 0.333...).
  • The set of rational numbers is denoted by the symbol 'Q'.
  • All integers are rational numbers because any integer n can be expressed as n/1.

Irrational Numbers

  • Irrational numbers cannot be expressed as a fraction p/q, where p and q are integers.
  • Their decimal representations are non-terminating and non-repeating.
  • Examples of irrational numbers: √2 (square root of 2), Ï€ (pi), e (Euler's number).
  • √2 is irrational because it cannot be written as a ratio of two integers. Its decimal representation goes on infinitely without repeating: 1.41421356...
  • Ï€ is the ratio of a circle's circumference to its diameter. Its decimal representation is also non-terminating and non-repeating: 3.14159265...
  • Irrational numbers are crucial in advanced mathematics, particularly in calculus and analysis.
  • The set of irrational numbers, combined with the set of rational numbers, makes up the set of real numbers.

Real Numbers

  • Real numbers include both rational and irrational numbers.
  • They can be visualized as points on a number line.
  • The set of real numbers is denoted by the symbol 'R'.
  • Real numbers can be used to measure continuous quantities.
  • Examples of real numbers: -5, 0, 1/2, √2, Ï€, 4.5, etc.
  • Real numbers are foundational in mathematical analysis, calculus, and many areas of physics and engineering.

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