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}