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

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

Vocabulary piecewise function step function

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).

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

Example 1: Consumer Application 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.

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) [5, ∞) Weights 5 and over

Example 1 Continued Step 2 Write a verbal description. 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.

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.

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.”

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.

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

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

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

Example 3A: Graphing Piecewise Functions Graph each function. 1 4 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.

Example 3A Continued For the first branch, the function is 3 when x = 0, so plot the point (0, 3) with an open circle and draw a ray with the slope 0.25 to the left. For the second branch, the function is 3 when x = 0, so plot the point (0, 3) with a solid dot and draw a ray with the slope of –2 to the right. O ●

Example 3B: Graphing Piecewise Functions Graph each function. x2 – 3 if x < 0 1 2 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.

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