Understanding Real Numbers

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Questions and Answers

Consider the number $x = a + b$, where $a$ is a non-zero rational number and $b$ is an irrational number. Which of the following statements is always true?

  • $x$ is a rational number.
  • $x$ is an integer.
  • $x$ is a natural number.
  • $x$ is an irrational number. (correct)

Two real numbers, $m$ and $n$, are such that their product $mn$ is irrational. Which of the following is necessarily true?

  • Both $m$ and $n$ are rational.
  • One of $m$ and $n$ is rational, and the other is irrational.
  • At least one of $m$ or $n$ is irrational. (correct)
  • Both $m$ and $n$ are irrational.

Which of the following operations, when performed on two irrational numbers, will always result in an irrational number?

  • Addition
  • Subtraction
  • Multiplication
  • None of the above (correct)

Let $x$ be a real number such that $x^2$ is rational and $x^3$ is irrational. Which of the following is a valid conclusion?

<p>$x$ is an irrational number. (B)</p> Signup and view all the answers

Given that $a$ and $b$ are rational numbers, and $x$ and $y$ are irrational numbers, which expression necessarily results in an irrational number?

<p>$(a + x)(b - y)$, where $a = -x$ and $b = y$ (D)</p> Signup and view all the answers

Which of the following intervals on the real number line contains both rational and irrational numbers?

<p>[$\pi, \pi + 0.01$] (C)</p> Signup and view all the answers

If $p$ and $q$ are distinct positive integers, which of the following expressions is always an integer?

<p>$\sqrt{p^2}$ (D)</p> Signup and view all the answers

Let $x$ be a real number such that $x + \frac{1}{x}$ is an integer. Which of the following statements must be true?

<p>It is possible for $x$ to be either rational or irrational. (B)</p> Signup and view all the answers

If $x$ and $y$ are real numbers such that $x + y$ is rational and $x - y$ is irrational, what can be concluded about $x$ and $y$?

<p>Both $x$ and $y$ can be expressed as the sum of a rational and an irrational number. (C)</p> Signup and view all the answers

Consider the number $0.12345678910111213...$, where the digits are formed by concatenating consecutive integers. Is this number rational or irrational?

<p>Irrational (A)</p> Signup and view all the answers

Which of the following numbers is irrational?

<p>$\sqrt{3}$ (A)</p> Signup and view all the answers

Which of the following statements is always true regarding the sum of a rational number and an irrational number?

<p>The sum is always irrational. (D)</p> Signup and view all the answers

If $a$ is a non-zero rational number and $b$ is an irrational number, what is the nature of the number $ab$?

<p>Always irrational (A)</p> Signup and view all the answers

If $x$ is a real number such that $x^2 - 2x$ is an integer, which of the following can be concluded about $x$?

<p>$x$ can be irrational. (D)</p> Signup and view all the answers

Determine which of the following expressions is equivalent to a rational number.

<p>$\sqrt{2} \cdot \sqrt{8}$ (C)</p> Signup and view all the answers

Which field of numbers contains every number that can be written as a decimal?

<p>Real Numbers (B)</p> Signup and view all the answers

If $x$ is a non-zero rational number and $y$ is an irrational number, then which of the following is always true?

<p>$\frac{x}{y}$ is irrational (A)</p> Signup and view all the answers

Given two integers, $a$ and $b$, where $a$ is positive and $b$ is negative, what can be said about the number $a/b$?

<p>It is always a rational number. (C)</p> Signup and view all the answers

If $x$ is a real number such that $x^3+1$ and $x^5+1$ are rational, is $x$ necessarily rational?

<p>Yes, $x$ must be rational. (A)</p> Signup and view all the answers

Suppose $a$ and $b$ are positive rational numbers such that $\sqrt{a}$ and $\sqrt{b}$ are irrational. Which of the following is necessarily irrational?

<p>$\sqrt{a} + \sqrt{b}$ (B)</p> Signup and view all the answers

Which set includes a number that is an integer, rational, and real?

<p>$\sqrt{9}$ (B)</p> Signup and view all the answers

Let $S$ be the set of all numbers of the form $a + b\sqrt{2}$, where $a$ and $b$ are rational numbers. Which of the following statements is true?

<p>$S$ is closed under addition and multiplication. (D)</p> Signup and view all the answers

Consider the sequence defined by $a_n = \frac{1}{n} - \frac{1}{n+1}$ for all positive integers $n$. What is the nature of the sum of the first $k$ terms of this sequence as $k$ approaches infinity?

<p>The sum approaches a rational number. (D)</p> Signup and view all the answers

If $x$ and $y$ are positive real numbers such that $x^2 + y^2 = 1$, what can be said about the nature of $x + y$?

<p>$x + y$ can be either rational or irrational, depending on the values of $x$ and $y$. (D)</p> Signup and view all the answers

Given that $x > 0$, is $x + \frac{1}{x}$ necessarily a rational number if $x$ is rational?

<p>Yes, it is always rational. (B)</p> Signup and view all the answers

Flashcards

Real Numbers

All numbers that can be represented on a number line.

Integers

Whole numbers that can be positive, negative, or zero.

Irrational Numbers

Cannot be expressed as a fraction p/q.

Rational Numbers

Can be expressed as a fraction p/q, where p and q are integers and q ≠ 0.

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Real Numbers

The set of all rational and irrational numbers combined.

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Rational * Irrational

The result is an irrational number.

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Integers are Rational

Integers can be expressed as a ratio with a denominator of 1.

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Sum/Difference/Product of Rationals

The result will always be a rational number.

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Quotient of Rationals

Result is a rational number, as long as you are not dividing by zero.

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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.
  • Examples of integers: -3, -2, -1, 0, 1, 2, 3.
  • Integers do not include fractions, decimals, or mixed numbers.

Rational Numbers

  • Rational numbers can be expressed as a fraction p/q, where p and q are integers and q ≠ 0.
  • They can be written as terminating or recurring decimals.
  • Examples of rational numbers: 0.5 (1/2), 0.333... (1/3), 5 (5/1).
  • All integers are rational numbers because they can be written as a fraction with a denominator of 1.
  • The sum, difference, and product of two rational numbers is always a rational number.
  • The quotient of two rational numbers is a rational number, provided that you are not dividing by zero.

Irrational Numbers

  • Irrational numbers cannot be expressed as a fraction p/q.
  • They have non-terminating and non-recurring decimal representations.
  • Examples of irrational numbers: √2, Ï€, e.
  • When performing calculations, irrational numbers are often left in surd form (e.g. √2 ) or represented by symbols (e.g. Ï€).
  • Approximations can be used for practical applications.
  • The set of all rational and irrational numbers combined makes up the set of real numbers.
  • Adding or multiplying a rational number (except 0) by an irrational number results in an irrational number.

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