1. EXAMPLE 2 Graphing Using Slope-Intercept Form The y -intercept is 3, so plot the point (0, 3).STEP 1 The slope is, so plot a second point by 1 2 STEP 2 moving up 1 unit and right 2 units. Draw a line through the points. STEP 3 Graph the equation y = x + 3. 1 2

2. EXAMPLE 3 Writing a Function Rule You are at the base of a trail on Mount Rainier in Washington. The temperature is 50.9 ° F. The temperature changes at a rate of –0.005 ° F per foot of elevation as you hike up. What is the temperature 1000 feet above the base? Hiking SOLUTION Write a verbal model. STEP 1

3. EXAMPLE 3 STEP 2 Write an algebraic model in slope-intercept form. The temperature changes at a rate of –0.005 ° F per foot, so m = 0.005. The initial temperature is 50.9 ° F, so b = 50.9. Let y be the temperature and x be the change in elevation. – Writing a Function Rule y = m x + b Write slope-intercept form. y = – 0.005 x + 50.9 Substitute –0.005 for m and 50.9 for b.

4. EXAMPLE 3 Writing a Function Rule STEP 3 Find the value of y when x = 1000. y = –0.005x + 50.9 Write the equation. = –0.005(1000) + 50.9 Substitute 1000 for x. = 45.9 Simplify. The temperature 1000 feet above the base is 45.9 ° F. ANSWER

5. GUIDED PRACTICE for Examples 2 and 3 Use the slope and y -intercept to graph the equation. 4. y = 2x + 5

6. GUIDED PRACTICE for Examples 2 and 3 5. y = 7x

7. GUIDED PRACTICE for Examples 2 and 3 6. – x + y = 6

8. GUIDED PRACTICE for Examples 2 and 3 7. What If? In Example 3, suppose the temperature at the base of the trail is 55.2 0 F. What is the temperature 2500 feet above the base? The temperature 2500 feet above the base is 42.7 ° F. ANSWER