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**Relations and Functions**

1-6 Relations and Functions Warm Up Lesson Presentation Lesson Quiz Holt Algebra 2

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**Do Now Use the graph for Problems 1–2.**

1. List the x-coordinates of the points. 2. List the y-coordinates of the points.

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Objectives TSW identify the domain and range of relations and functions. TSW determine whether a relation is a function.

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Vocabulary relation domain range function

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**A relation is a pairing of input values with output values**

A relation is a pairing of input values with output values. It can be shown as a set of ordered pairs (x,y), where x is an input and y is an output. The set of input values for a relation is called the domain, and the set of output values is called the range.

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Mapping Diagram Domain Range A 2 B C Set of Ordered Pairs {(2, A), (2, B), (2, C)} (x, y) (input, output) (domain, range)

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**Example 1: Identifying Domain and Range**

Give the domain and range for this relation: {(100,5), (120,5), (140,6), (160,6), (180,12)}. List the set of ordered pairs: Domain: Range:

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Example 2 Give the domain and range for the relation shown in the graph. List the set of ordered pairs:

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Suppose you are told that a person entered a word into a text message using the numbers 6, 2, 8, and 4 on a cell phone. It would be difficult to determine the word without seeing it because each number can be used to enter three different letters.

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**Number {Number, Letter} {(6, M), (6, N), (6, O)}**

The numbers 6, 2, 8, and 4 each appear as the first coordinate of three different ordered pairs. {(6, M), (6, N), (6, O)} {(2, A), (2, B), (2, C)} {(8, T), (8, U), (8, V)} {(4, G), (4, H), (4, I)}

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However, if you are told to enter the word MATH into a text message, you can easily determine that you use the numbers 6, 2, 8, and 4, because each letter appears on only one numbered key. The first coordinate is different in each ordered pair. {(M, 6), (A, 2), (T, 8), (H,4)} A relation in which the first coordinate is never repeated is called a function. In a function, there is only one output for each input, so each element of the domain is mapped to exactly one element in the range.

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Although a single input in a function cannot be mapped to more than one output, two or more different inputs can be mapped to the same output.

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Not a function: The relationship from number to letter is not a function because the domain value 2 is mapped to the range values A, B, and C. Function: The relationship from letter to number is a function because each letter in the domain is mapped to only one number in the range.

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**Example 3: Determining Whether a Relation is a Function**

Determine whether each relation is a function. A. from the items in a store to their prices on a certain date B. from types of fruits to their colors

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Example 4 Determine whether each relation is a function. A. B. from the number of items in a grocery cart to the total cost of the items in the cart

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Every point on a vertical line has the same x-coordinate, so a vertical line cannot represent a function. If a vertical line passes through more than one point on the graph of a relation, the relation must have more than one point with the same x-coordinate. Therefore the relation is not a function.

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**Example 5: Using the Vertical-Line Test**

Use the vertical-line test to determine whether the relation is a function. If not, identify two points a vertical line would pass through.

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**Example 6: Using the Vertical-Line Test**

Use the vertical-line test to determine whether the relation is a function. If not, identify two points a vertical line would pass through.

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Example 7 Use the vertical-line test to determine whether the relation is a function. If not, identify two points a vertical line would pass through.

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Example 8 Use the vertical-line test to determine whether the relation is a function. If not, identify two points a vertical line would pass through. This is not a function. A vertical line at x = 1 would pass through (1, 2) and (1, –2).

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Lesson Quiz: Part I 1. Give the domain and range for this relation: {(10, 5), (20, 5), (30, 5), (60, 100), (90, 100)}. Determine whether each relation is a function. 2. from each person in class to the number of pets he or she has 3. from city to zip code

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Lesson Quiz: Part II Use the vertical-line test to determine whether the relation is a function. If not, identify two points a vertical line would pass through. 4.

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Lesson Quiz: Part I 1. Give the domain and range for this relation: {(10, 5), (20, 5), (30, 5), (60, 100), (90, 100)}. Determine whether each relation is a function. 2. from each person in class to the number of pets he or she has 3. from city to zip code D: {10, 20, 30, 60, 90)} R: {5, 100} function not a function

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Lesson Quiz: Part II Use the vertical-line test to determine whether the relation is a function. If not, identify two points a vertical line would pass through. 4. not a function; possible answer: (3, 2) and (3, –2)

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