Natural Numbers and Integer Properties Quiz

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Questions and Answers

Which property of natural numbers ensures that the sum of any two natural numbers is also a natural number?

  • Associative Property of Addition
  • Commutative Property of Addition
  • Distributive Property of Multiplication over Addition
  • Closure Property of Addition (correct)

What property is illustrated by the equation $a + (b + c) = (a + b) + c$ for natural numbers a, b, and c?

  • Distributive Property of Multiplication over Addition
  • Associative Property of Addition (correct)
  • Commutative Property of Addition
  • Closure Property of Addition

Which property of natural numbers states that the product of any two natural numbers is also a natural number?

  • Multiplicative Identity Property
  • Commutative Property of Multiplication
  • Associative Property of Multiplication
  • Closure Property of Multiplication (correct)

What property is represented by the equation $a \cdot (b + c) = a \cdot b + a \cdot c$ for natural numbers a, b, and c?

<p>Distributive Property of Multiplication over Addition (B)</p> Signup and view all the answers

Which of the following is NOT a property of integers?

<p>Trichotomy Law (D)</p> Signup and view all the answers

What property of the integers ensures the existence of a unique number called the multiplicative identity?

<p>Multiplicative Identity Property (D)</p> Signup and view all the answers

Which property of integers states that the order in which numbers are added doesn't change the result?

<p>Commutative Property of Addition (A)</p> Signup and view all the answers

What is the set of integer numbers denoted by?

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

Which property states that for any two integers, their product is also an integer?

<p>Closure Property of Multiplication (A)</p> Signup and view all the answers

What does the Additive Inverse Property state for all integers?

<p>The sum of any integer and its negative is zero. (A)</p> Signup and view all the answers

Which property guarantees that for any integers a, b and c, the equation a · (b + c) = a · b + a · c is always true?

<p>Distributive Property of Multiplication over Addition (D)</p> Signup and view all the answers

Which property states that the order in which you multiply two integers does not affect the result?

<p>Commutative Property of Multiplication (B)</p> Signup and view all the answers

Which of the following properties is NOT applicable to rational numbers?

<p>Multiplicative Inverse Property (D)</p> Signup and view all the answers

Which property allows us to group integers in multiplication without changing the outcome?

<p>Associative Property of Multiplication (B)</p> Signup and view all the answers

Which property states that for any integer 'a', there is a unique integer '-a' such that their sum is zero?

<p>Additive Inverse Property (A)</p> Signup and view all the answers

Which property guarantees that for any two numbers, there is a unique number that, when added to the first number, results in the second number?

<p>Closure Property of Addition (D)</p> Signup and view all the answers

Which of the following inequalities is true for all positive integers n?

<p>$n^2 &gt; 3n$ (D)</p> Signup and view all the answers

What is the value of n for which the following inequality is true: $\frac{1}{4} + \frac{1}{9} + ... + \frac{1}{n^2} ≤ 2 - \frac{1}{n}$ ?

<p>4 (D)</p> Signup and view all the answers

What is the value of the expression $(1 + x)^n$ for a real number x > -1 and a positive integer n, according to Bernoulli's Identity?

<p>$1 + nx$ (D)</p> Signup and view all the answers

For what nonnegative integers n is the expression $5n-1$ divisible by 4?

<p>All nonnegative integers (D)</p> Signup and view all the answers

For what nonnegative integers n is the expression $10^{n+1} - 9^n - 10$ divisible by 81?

<p>All nonnegative integers (B)</p> Signup and view all the answers

For what nonnegative integers n is the expression $32^n - 2^n$ divisible by 7?

<p>All nonnegative integers (A)</p> Signup and view all the answers

What is the base case for the following statement: For every nonnegative integer n, 2n > n?

<p>n = 0 (B)</p> Signup and view all the answers

Which of the following is the correct inductive step for the statement: For every nonnegative integer n, 2n > n?

<p>Assume 2k &gt; k. Then 2(k+1) = 2k + 2 &gt; k + 2 &gt; k + 1. (B)</p> Signup and view all the answers

What is the minimum counterexample that can be used to prove that 6 | 7n(n^2 - 1) for every positive integer n?

<p>3 (D)</p> Signup and view all the answers

What is the minimum counterexample for the statement that 3|(2^$2n$ - 1) for every positive integer n?

<p>1 (B)</p> Signup and view all the answers

What is the base case for the statement: For every integer n ≥ 5, 2n > n^2?

<p>n = 5 (C)</p> Signup and view all the answers

Which of the following is the correct inductive step for the statement: For every integer n ≥ 5, 2n > n^2?

<p>Assume 2k &gt; k^2. Then 2(k+1) = 2k + 2 &gt; k^2 + 2 &gt; (k+1)^2. (A), Assume 2k &gt; k^2. Then 2(k+1) = 2k + 2 &gt; k^2 + 2 &gt; (k+1)^2. (B)</p> Signup and view all the answers

What is the base case for the statement: For every nonnegative integer n, 3 | (2^(2n) - 1)?

<p>n = 0 (D)</p> Signup and view all the answers

Which of the following is the correct inductive step for the statement: For every nonnegative integer n, 3 | (2^(2n) - 1)?

<p>Assume 3 | (2^(2k) - 1). Then 3 | (2^(2k) - 1) * 4 = 2^(2(k+1)) - 4 . Then 3 | (2^(2(k+1)) - 4 + 3) = 2^(2(k+1)) - 1. (B)</p> Signup and view all the answers

Which of the following set(s) is/are well-ordered?

<p>S = {−2, −1, 0, 1, 2} (A), S = {p : p is a prime} = {2, 3, 5, 7, 11, 13, 17,...} (B)</p> Signup and view all the answers

Which of the following statements accurately describes the result of adding 1 + 3 + 5 + · · · + (2n − 1) and (2n − 1) + (2n − 3) + · · · + 1 ?

<p>The sum is equal to 2n^2. (A)</p> Signup and view all the answers

Which of the following is the correct formula for 1 + 4 + 7 + · · · + (3n − 2) for positive integers n?

<p>n(3n - 1) (A)</p> Signup and view all the answers

What does 13 + 23 + 33 +...+ n3 represent geometrically?

<p>The total number of cubes in a n x n x n cube (D)</p> Signup and view all the answers

Which of the following formulas represents the sum 1 · 3 + 2 · 4 + 3 · 5 +...+ n(n + 2) for every positive integer n?

<p>n(n + 1)(2n + 7)/6 (A)</p> Signup and view all the answers

Given that r ̸= 1 is a real number, which of the following formulas represents the sum a + ar + ar 2 +...+ ar n−1 for every positive integer n?

<p>a(1 − r n )/(1−r) (C)</p> Signup and view all the answers

Consider the following sequence: 1/3·4 + 1/4·5 + 1/5·6 + … + 1/(n + 2)(n + 3). Which of the following formulas represents the sum of this sequence for every positive integer n?

<p>n/(3n + 9) (C)</p> Signup and view all the answers

For which integer values of n is the inequality 2n > n3 true?

<p>n ≥ 10 (A)</p> Signup and view all the answers

What is the name given to the number 1 in the Multiplicative Identity Property?

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

Which property states 'For all a, b, c ∈ Q, if a < b and c > 0, then ac < bc'?

<p>Closure Under Multiplication (C)</p> Signup and view all the answers

What is the set of all rational and irrational numbers called?

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

Which of the following is NOT an irrational number?

<p>3/4 (B)</p> Signup and view all the answers

What is the 'Well-Ordering Axiom'?

<p>Every nonempty subset of N contains a smallest element. (C)</p> Signup and view all the answers

What is the first step in proving a statement using the Principle of Mathematical Induction?

<p>Show that the statement P(1) is true. (A)</p> Signup and view all the answers

What is the formula for the sum of the first n squares?

<p>$n(n+1)(2n+1)/6$ (D)</p> Signup and view all the answers

What is the starting value for proving the statement '1 + 2 + 3 +...+ n = n(n+1)/2' using mathematical induction?

<p>n = 1 (D)</p> Signup and view all the answers

Flashcards

Additive Identity Property

For all integers a, a + 0 = a, with 0 being unique.

Additive Inverse Property

For every integer a, there exists -a such that a + (-a) = 0.

Closure Property of Multiplication

For all integers a and b, a · b is also an integer.

Commutative Property of Multiplication

For all integers a and b, a · b = b · a.

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Associative Property of Multiplication

For all integers a, b, c, a · (b · c) = (a · b) · c.

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Multiplicative Identity Property

There is a unique integer 1 such that a · 1 = a, and 1 is not 0.

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Distributive Property of Multiplication

For all integers a, b, c, a · (b + c) = a · b + a · c.

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Trichotomy Law

For any integers a and b, exactly one of a = b, a > b, or a < b holds.

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Natural Numbers

The set of positive integers starting from 1, denoted as N = {1, 2, 3,...}.

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Closure Property of Addition (Natural Numbers)

For all a, b ∈ N, a + b ∈ N.

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Commutative Property of Addition

For all a, b ∈ N, a + b = b + a.

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Associative Property of Addition

For all a, b, c ∈ N, a + (b + c) = (a + b) + c.

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Closure Property of Multiplication (Natural Numbers)

For all a, b ∈ N, a · b ∈ N.

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Multiplicative Inverse Property

For each a ∈ Q with a ≠ 0, there exists a unique 1/a such that a · (1/a) = 1.

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Well-Ordering Axiom

Every nonempty subset of natural numbers N has a smallest element.

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Principle of Mathematical Induction

If P(1) is true and P(k) implies P(k+1), then P(n) is true for all positive integers n.

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Closure Under Addition

For all a, b, c ∈ Q, if a < b, then a + c < b + c.

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Closure Under Multiplication

For all a, b, c ∈ Q, if a < b and c > 0, then ac < bc.

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Irrational Numbers

Numbers that cannot be expressed as a fraction a/b, where a and b are integers, b ≠ 0.

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Law of Transitivity

For all a, b, c ∈ Q, if a < b and b < c, then a < c.

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Closure Property Summary

Both addition and multiplication maintain closure in rational numbers.

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Recursive Sequence

A sequence defined based on preceding terms.

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Well-Ordered Set

Every non-empty subset has a least element.

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Mathematical Induction

A proof technique to show a statement holds for all integers.

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Sum of Odd Numbers

The sum 1 + 3 + 5 + ... + (2n - 1) equals n^2.

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Sum of Even Sequence

1 + 5 + 9 + ... + (4n - 3) equals 2n^2 - n.

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Sum of Cubes

1³ + 2³ + ... + n³ equals (n(n+1)/2)².

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Finite Geometric Series

Sum of a finite geometric series equals a(1 - r^n) / (1 - r).

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Factorial Growth

n! grows faster than polynomial functions for large n.

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Bernoulli's Identity

For x > -1, (1 + x)^n ≥ 1 + nx for positive n.

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Divisibility by 4

Prove 4 divides (5n − 1) for nonnegative n.

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Divisibility by 81

Prove 81 divides (10^(n+1) − 9^n − 10) for nonnegative n.

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Fibonacci Sequence

Defined as F1 = 1, F2 = 1, Fn = Fn-1 + Fn-2 for n ≥ 3.

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Minimum Counterexample Method

A proof strategy involving counterexamples to prove divisibility properties.

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Divisibility by 3

Prove 3 divides (22n − 1) for positive n.

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Recursive Sequence Definition

Define sequences using previous terms for clarity.

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Conjecture Verification

Formulate and verify the formula for a sequence based on initial terms.

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Base Case

The initial step that confirms the statement is true for the first integer.

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Inductive Step

The part of the proof showing that if the statement holds for n, it holds for n+1.

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Strong Induction

An induction method requiring P(i) for all i up to k to prove P(k+1).

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Implication in Induction

A logical statement connecting assumptions to conclusions in a proof.

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Verification of Conjectures

Proving a proposed statement or formula true through examples or proof.

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Divisibility in Induction

A property that shows one integer can be divided by another without a remainder.

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Study Notes

Unit One: Math 151

  • This unit covers foundational mathematical concepts, specifically number theory, the principle of mathematical induction, and related topics.
  • The presenter is Yao Eliken Ayekple (PhD), from KNUST.
  • The date of the presentation is January 17, 2024.

Introduction to Number Theory

  • 1.1 Real Numbers:
    • Natural Numbers (N): The set of natural numbers, N, includes positive integers and is represented as {1, 2, 3, ...}.
    • Properties of Natural Numbers: Addition (+) and multiplication (â‹…) are discussed. Key properties include closure, commutative, associative, distributive and multiplicative identity properties.
    • Closure Property of Addition: For any natural numbers 'a' and 'b', (a + b) is also a natural number.
    • Commutative Property of Addition: a + b = b + a
    • Associative Property of Addition: a + (b + c) = (a + b) + c
    • Closure Property of Multiplication: For any natural numbers 'a' and 'b', (a â‹… b) is also a natural number.
    • Commutative Property of Multiplication: a â‹… b = b â‹… a
    • Associative Property of Multiplication: a â‹… (b â‹… c) = (a â‹… b) â‹… c
    • Multiplicative Identity Property: a â‹… 1 = a
    • Distributive Property of Multiplication over Addition: a â‹… (b + c) = a â‹… b + a â‹… c
    • Trichotomy Law: For any natural numbers 'a' and 'b', exactly one of the following is true: a = b, a > b, or a < b.
    • Law of Transitivity: If a < b and b < c, then a < c.
    • Closure under Addition: If a < b, then a + c < b + c.
    • Closure under Multiplication: If a < b and c > 0, then ac < bc.
  • Integers (Z): The set of integers, Z, includes positive and negative integers and zero. {..., -3, -2, -1, 0, 1, 2, 3,...}
    • Properties of Integers: Closure, commutative, associative, additive identity, additive inverse, multiplicative identity.
    • Basic properties of addition and multiplication on integers are outlined.
  • Rational Numbers (Q): The set of rational numbers, Q, is defined as the set of all numbers that can be expressed as a fraction p/q where p and q are integers, and q ≠ 0.
    • Properties of Rational Numbers: Closure, commutative, associative, additive identity, additive inverse, multiplicative identity, multiplicative inverse.
  • Irrational Numbers: Numbers that cannot be expressed as a fraction p/q, where p and q are integers, and q ≠ 0. Such numbers as √2, Ï€ and e.

The Principle of Mathematical Induction

  • Principle of Mathematical Induction: A method for proving statements about all positive integers. Two forms are shown.
    • Base case: Prove that the statement holds for a starting integer (often 1).
    • Inductive step: Prove that if the statement holds for any arbitrary positive integer k, then it also holds for k + 1.
  • Examples: Illustrative examples are provided to demonstrate applications.

Further Topics (Questions/Exercises)

  • Mathematical induction is used to solve a variety of problems.

  • Specific problems are provided for the learner's practice in solving problems involving induction. These include proving various identities and statements involving sequences, sums or products of integers.

  • Strong principle of mathematical induction is also presented and applied to complex examples.

Recursive Sequences

  • A number of recursive examples involving sequences are covered.

Well-Ordering Axiom

  • Introduced as a property of some sets of numbers (positive integers).

Additional Exercises/Problems

  • A set of practice questions is included for various problems, applying different methods.

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