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Intervals and absolute value are key concepts in understanding the real number system. They help us visualize and manipulate sets of numbers on the number line. These tools are essential for solving equations and inequalities, and for representing subsets of real numbers.

Mastering intervals and absolute value provides a foundation for more advanced mathematical analysis. By grasping these concepts, you'll be better equipped to tackle complex problems involving real numbers and their properties in future math courses.

Interval Types and Notation

Types of Intervals

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  • Open intervals do not include their endpoints and are denoted using parentheses (a, b)
  • Closed intervals include both endpoints and are denoted using square brackets [a, b]
  • Half-open intervals include only one endpoint and are denoted using a combination of a parenthesis and a square bracket (a, b] or [a, b)
  • Intervals can be bounded having both upper and lower bounds (0, 1) or unbounded having only one or no bounds (0, ∞)
  • Intervals can be classified as finite having a specific length [0, 1] or infinite extending indefinitely in one or both directions (-∞, ∞)

Defining and Classifying Intervals

  • An interval is a set of real numbers that includes all numbers between any two numbers in the set
  • Intervals are defined by their endpoints and whether those endpoints are included or excluded
  • The type of bracket used to denote an interval indicates whether the endpoint is included (square bracket) or excluded (parenthesis)
  • Classifying intervals as open, closed, half-open, bounded, unbounded, finite, or infinite helps to understand the properties and characteristics of the set of numbers represented by the interval

Absolute Value: Concept and Geometry

Concept of Absolute Value

  • The absolute value of a real number is its distance from zero on the real number line, regardless of its sign
  • The absolute value of a number a is denoted as |a|
  • For any real number a, |a| ≥ 0, and |a| = 0 if and only if a = 0
  • The absolute value of a number is always non-negative, as it represents a distance (-3 and 3 both have an absolute value of 3)

Geometric Interpretation of Absolute Value

  • Geometrically, the absolute value of a number represents the length of the line segment from the origin to the point representing that number on the real number line
  • On a number line, the absolute value of a number is the distance between that number and zero, regardless of the direction
  • The graph of y = |x| is a V-shaped graph with the vertex at the origin (0, 0) and the two rays extending symmetrically in the positive y-direction
  • The graph of y = |x - a| + b represents a vertical shift of the basic absolute value graph by a units horizontally and b units vertically

Absolute Value: Solving Equations and Inequalities

Properties of Absolute Value

  • For any real numbers a and b, |a| = |b| if and only if a = b or a = -b
  • The absolute value of a product is equal to the product of the absolute values: |ab| = |a||b|
  • The absolute value of a quotient is equal to the quotient of the absolute values: |a/b| = |a|/|b|, where b ≠ 0
  • The absolute value of a sum is less than or equal to the sum of the absolute values: |a + b| ≤ |a| + |b| (triangle inequality)

Solving Absolute Value Equations and Inequalities

  • To solve an absolute value equation, consider the two possible cases: the positive and negative values of the expression inside the absolute value symbols
  • For example, to solve |x - 3| = 5, consider x - 3 = 5 and x - 3 = -5, which leads to x = 8 or x = -2
  • To solve an absolute value inequality, consider the distance between the expression inside the absolute value symbols and the number on the other side of the inequality sign
  • For example, to solve |x - 2| < 3, consider -3 < x - 2 < 3, which leads to -1 < x < 5

Representing Subsets of Real Numbers

Interval Notation

  • Interval notation is a way to represent a set of real numbers using parentheses, square brackets, and infinity symbols
  • In interval notation, a square bracket is used to indicate that the endpoint is included in the set [a, b], while a parenthesis is used to indicate that the endpoint is not included (a, b)
  • Infinity symbols (∞ and -∞) are used to represent unbounded intervals, such as (0, ∞) or (-∞, -2]
  • Examples of intervals in interval notation: [0, 1], (2, 5], (-∞, 0), [3, ∞)

Set-Builder Notation

  • Set-builder notation is a way to describe a set by stating the properties that its elements must satisfy
  • In set-builder notation, the set is denoted as {x | P(x)}, where x is a variable representing an element of the set, and P(x) is a statement describing the properties that x must satisfy to be included in the set
  • Set-builder notation can be used to represent intervals, as well as more complex subsets of real numbers that cannot be easily represented using interval notation
  • Examples of sets in set-builder notation: {x | x ∈ ℝ, x ≥ 0}, {x | x ∈ ℤ, -3 ≤ x < 5}, {x | x ∈ ℝ, x² < 9}


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© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
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