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Piecewise Functions. 6-3. Warm Up. Lesson Presentation. Lesson Quiz. Holt McDougal Algebra 2. Holt Algebra 2. Answers. Equation -3 (4x+2i)(4x-2i) (3x+7i)(3x-7i) (-1,1)(-5,-3) (5,-3) (-1,3) (1,3) (-3,-1). 1. 2. 1. y = – x + 43. 2. Warm Up

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6-3

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  1. Piecewise Functions 6-3 Warm Up Lesson Presentation Lesson Quiz Holt McDougal Algebra 2 Holt Algebra 2

  2. Answers • Equation -3 • (4x+2i)(4x-2i) • (3x+7i)(3x-7i) • (-1,1)(-5,-3) • (5,-3) (-1,3) • (1,3) (-3,-1)

  3. 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)

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

  5. Vocabulary piecewise function step function

  6. 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).

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

  8. Example 1: Consumer Application Create a table and a verbal description to represent the graph.

  9. Example 1 Continued The domain of the function is divided into three intervals: Weights under 2 [0, 2) Weights 2 and under 5 [2, 5) Weights 5 and over [5, ∞) Mixed nuts cost $8.00 per pound for less than 2 lb, $6.00 per pound for 2 lb or more and less than 5 lb, and $5.00 per pound for 5 or more pounds.

  10. You Try 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.

  11. You Try Example 1 Continued The domain of the function is divided into three intervals: [8, 12) $28 [12, 4) $24 [4, 9) $12

  12. You Try 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.

  13. 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 could be.

  14. 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.”

  15. 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.

  16. Example 2A: Evaluating a Piecewise Function Evaluate each piecewise function for x = –1 and x = 4. 2x + 1 if x ≤ 2 h(x) = x2 – 4 if x > 2 Because –1 ≤ 2, use the rule for x ≤ 2. h(–1) = 2(–1) + 1 = –1 Because 4 > 2, use the rule for x > 2. h(4) = 42 – 4 = 12

  17. g(–1) = 2(–1) = 1 2 Example 2B: Evaluating a Piecewise Function 2x if x ≤ –1 g(x) = 5x if x > –1 Because –1 ≤ –1, use the rule for x ≤ –1. Because 4 > –1, use the rule for x > –1. g(4) = 5(4) = 20

  18. You Try 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

  19. You Try 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

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

  21. 1 4 Example 3A: Graphing Piecewise Functions Graph each function. x + 3 if x < 0 g(x) = –2x + 3 if x ≥ 0 The function is composed of two linear pieces that will be represented by two rays. Because the domain is divided by x = 0, evaluate both branches of the function at x = 0.

  22. Example 3A Continued ● O

  23. 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.

  24. 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

  25. 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.

  26. 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.

  27. Assignment: worksheet B

  28. Answers From Worksheet B 7. 10, -1 8. -10, - 3 9. 5, 2 10. – 12, 28

  29. 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.

  30. Example 4: Sports Application Jennifer is completing a 15.5-mile triathlon. She swims 0.5 mile in 30 minutes, bicycles 12 miles in 1 hour, and runs 3 miles in 30 minutes. Sketch a graph of Jennifer’s distance versus time. Then write a piecewise function for the graph. Swimming: 0 ≤ t ≤ 0.5 Biking: 0.5 < t ≤ 1.5 Running: 1.5 < t ≤ 2

  31. Example 4 Continued Step 3 Graph the function. After 30 minutes, Jennifer has covered 0.5 miles. On the next leg, she reaches a distance of 12 miles after a total of 1.5 hours. Finally she completes the 15.5 miles after 2 hours.

  32. Example 4 Continued Step 4 Write a linear function for each leg. Use point-slope form: y – y1 = m(x – x1). Swimming: d = t Use m = 0.5 and (0, 0). Biking: d = 12t – 5.5 Use m = 12 and (0.5, 0.5). Use m = 6 and (1.5, 12.5). Running: d = 6t + 3.5 t if 0 ≤ t ≤ 0.5 12t – 5.5 if 0.5 < t ≤ 1.5 The function rule is d(t) = 6t + 3.5 if 1.5 < t ≤ 2

  33. Ticket Out 1. Write and graph a piecewise function for the following situation. A house painter charges $12 per hour for the first 40 hours he works, time and a half for the 10 hours after that, and double time for all hours after that. How much does he earn for a 70-hour week? 18x-240=18(x-40)+((12)(40)) 24x-540=24(x-50)+((12)(40)+(18)(50))

  34. Assignment: Practice C

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