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Piecewise Functions. 9-2. Warm Up. Lesson Presentation. Lesson Quiz. Holt Algebra 2. 1. 2. 1. y = – x + 43. 2. Warm Up Write the equation of each line in slope-intercept form. 1. slope of 3 and passes through the point (50, 200). y = 3 x + 50.

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9-2

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  1. Piecewise Functions 9-2 Warm Up Lesson Presentation Lesson Quiz Holt Algebra 2

  2. 1 2 1 y = – x + 43 2 Warm Up Write the equation of each line in slope-intercept form. 1. slope of 3 and passes through the point (50, 200) y = 3x + 50 2. slope of – and passes through the point (6, 40)

  3. Objectives Write and graph piecewise functions. Use piecewise functions to describe real-world situations.

  4. Vocabulary piecewise function step function

  5. A piecewise function is a function that is a combination of one or more functions. The rule for a piecewise function is different for different parts, or pieces, of the domain. For instance, movie ticket prices are often different for different age groups. So the function for movie ticket prices would assign a different value (ticket price) for each domain interval (age group).

  6. Remember! When using interval notation, square brackets [ ] indicate an included endpoint, and parentheses ( ) indicate an excluded endpoint. (Lesson 1-1)

  7. Check It Out! Example 1 Create a table and a verbal description to represent the graph. Step 1 Create a table Because the endpoints of each segment of the graph identify the intervals of the domain, use the endpoints and points close to them as the domain values in the table.

  8. Check It Out! Example 1 Continued The domain of the function is divided into three intervals: [8, 12) $28 [12, 4) $24 [4, 9) $12

  9. Check It Out! Example 1 Continued Step 2 Write a verbal description. The green fee is $28 from 8 A.M. up to noon, $24 from noon up to 4 P.M., and $12 from 4 up to 9 P.M.

  10. A piecewise function that is constant for each interval of its domain, such as the ticket price function, is called a step function. You can describe piecewise functions with a function rule. The rule for the movie ticket prices from Example 1 on page 662 is shown.

  11. Read this as “f of x is 5 if x is greater than 0 and less than 13, 9 if x is greater than or equal to 13 and less than 55, and 6.5 if x is greater than or equal to 55.”

  12. To evaluate any piecewise function for a specific input, find the interval of the domain that contains that input and then use the rule for that interval.

  13. Check It Out! Example 2a Evaluate each piecewise function for x = –1 and x = 3. 12 if x < –3 15 if –3 ≤ x < 6 f(x) = 20 if x ≥ 6 Because –3 ≤ –1 < 6, use the rule for –3 ≤ x < 6 . f(–1) = 15 Because –3 ≤ 3 < 6, use the rule for –3 ≤ x < 6 . f(3) = 15

  14. Check It Out! Example 2b Evaluate each piecewise function for x = –1 and x = 3. 3x2 + 1 if x < 0 g(x) = 5x –2 if x ≥ 0 Because –1 < 0, use the rule for x < 0. g(–1) = 3(–1)2 + 1 = 4 Because 3 ≥ 0, use the rule for x ≥ 0. g(3) = 5(3) – 2 = 13

  15. You can graph a piecewise function by graphing each piece of the function.

  16. Check It Out! Example 3a Graph the function. 4 if x ≤ –1 f(x) = –2 if x > –1 The function is composed of two constant pieces that will be represented by two rays. Because the domain is divided by x = –1, evaluate both branches of the function at x = –1.

  17. Check It Out! Example 3a Continued The function is 4 when x ≤–1, so plot the point (–1, 4) with a closed circle and draw a horizontal ray to the left. The function is –2 when x > –1, so plot the point (–1, –2) with an open circle and draw a horizontal ray to the right. ● O

  18. Check It Out! Example 3b Graph the function. –3x if x < 2 g(x) = x + 3 if x ≥ 2 The function is composed of two linear pieces. The domain is divided at x = 2.

  19. Check It Out! Example 3b Continued ● O Add an open circle at (2, –6) and a closed circle at (2, 5) and so that the graph clearly shows the function value when x = 2.

  20. d t Remember! The distance formula d = rt can be arranged to find rates: r = . Notice that piecewise functions are not necessarily continuous, meaning that the graph of the function may have breaks or gaps. To write the rule for a piecewise function, determine where the domain is divided and write a separate rule for each piece. Combine the pieces by using the correct notation.

  21. Check It Out! Example 4 Shelly earns $8 an hour. She earns $12 an hour for each hour over 40 that she works. Sketch a graph of Shelly’s earnings versus the number of hours that she works up to 60 hours. Then write a piecewise function for the graph. Step 1 Make a table to organize the data.

  22. Check It Out! Example 4 Continued Step 2 Because the number of hours worked is the independent variable, determine the intervals for the function. She works equal to or less than 40 hours. 0 ≤ h ≤ 40 She works more than 40 hours. h > 40

  23. Check It Out! Example 4 Continued Step 3 Graph the function. Shelly earns $8 per hour for 0–40. After 40 hours, she earns $12 per hour.

  24. Check It Out! Example 4 Continued Step 4 Write a linear function for each leg. Use a point-slope form: y – y1 = m(x – x1). 0–40 hours: 8h Use m = 8. Hours > 40: 12(h – 4) + 320 Use m = 12 and (40, 320). 8h if 0 ≤ h ≤ 40 The function rule is f(h) = 12(h – 40) + 320 if h > 40

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