Warm Up Write the equation of each line in slope-intercept form.

1. 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)

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

3. Vocabulary piecewise function step function

4. 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).

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

6. Example 1 The domain of the function is divided into three intervals: [0, 2) Weights under 2 Weights 2 and under 5 [2, 5) [5, ∞) Weights 5 and over

7. Example 1 Create a table and a verbal description to represent the graph. 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. Example 2 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.

9. Example 2 Continued The domain of the function is divided into three intervals: [8, 12) $28 [12, 4) $24 [4, 9) $12

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. 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.”

11. Example 3 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. 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

12. Example 4 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

13. 1 2 Example 5 Graph each function. x2 – 3 if x < 0 x – 3 if 0 ≤ x < 4 g(x) = (x – 4)2 – 1 if x ≥ 4 The function is composed of one linear piece and two quadratic pieces. The domain is divided at x = 0 and at x = 4.

14. Example 5 Continued No circle is required at (0, –3) and (4, –1) because the function is connected at those points.

15. Example 6 Graph the function. 4 if x ≤ –1 ● f(x) = –2 if x > –1 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

16. Example 6: 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.

17. Example 6 Continued Step 1 Make a table to organize the data. Use the distance formula to find Jennifer’s rate for each leg of the race.

18. Example 6 Continued Step 2 Because time is the independent variable, determine the intervals for the function. Swimming: 0 ≤ t ≤ 0.5 She swims for half an hour. Biking: 0.5 < t ≤ 1.5 She bikes for the next hour. Running: 1.5 < t ≤ 2 She runs the final half hour.

19. Example 6 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.

20. Example 6 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

21. Independent Practice Due Tomorrow at Beginning of Class p. 426 # 9-18 all

22. x2 + 2 if x ≤ 2 x + 3 if x > 2 1 1 2 2 Lesson Quiz: Part I 1. Graph the function, and evaluate at x = 1 and x = 3. p(x) =

23. Lesson Quiz: Part II 2. 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?