Review Videos

1. Review Videos • Graphing the x and y intercept • Graphing the x and y intercepts • Graphing a line in slope intercept form • Converting into slope intercept form

2. Chapter 7 Section 6 Families of Linear Graphs

3. What You’ll Learn You’ll learn to explore the effects of changing the slopes and y-intercepts of linear functions.

4. Why It’s Important Business Families of graphs can display different fees.

5. Families of linear graphs often fall into two categories- • Those with the same slope 2. Those with the same y-intercept.

6. Family of Graphs What do these lines have in common? y = ½x + 3 y = ½x - 1 Same Slope

7. Family of Graphs What do these lines have in common? y = ⅓x + 1 y = -x + 1 Same y-intercept

8. Not a Family of Graphs What do these lines have in common? y = x + 2 y = ⅓x Different y-intercept and slope

9. Example 1 Graph each pair of equations. Describe any similarities or differences. Explain why they are a family of graphs. y = 3x + 4 y = 3x – 2 The graphs have y-intercepts of 4 and -2, respectively. They are a family of graphs because the slope of each line is 3. y = 3x + 4 y = 3x - 2

10. Example 2 Graph each pair of equations. Describe any similarities or differences. Explain why they are a family of graphs. y = x + 3 y = -½x + 3 Each graph has a different slope. Each graph has a y-intercept of 3. Thus, they are a family of graphs. y = -½x + 3 y = x + 3

11. Hint: You can compare graphs of lines by looking at their equations.

12. Example 3 • Matthew and Juan are starting their own pet care business. Juan wants to charge $5 an hour. Matthew thinks they should charge $3 an hour. Suppose x represents the number of hours. Then y = 5x and y = 3x represents how much they would charge, respectively. Compare and contrast the graphs of the equations. 6 The equations have the same y-intercept, but the graph of y = 5x is steeper. This is because its slope, which represents $5 per hour, is greater that the slope of the graph of y = 3x. y = 5x 5 y = 3x 4 3 2 0 .5 1 1.5 2

13. Your Turn Compare and contrast the graphs of the equations. Verify by graphing the equation. y = -3x + 4 y = -x + 4

14. Answer y = -3x + 4 y = -x + 4 Same y-intercept Different slope y = -x + 4 y = -3x + 4

15. Try This One Compare and contrast the graphs of the equations. Verify by graphing the equation. y = ⅔x + 3 y = ⅔x -1

16. Answer y = ⅔x + 3 y = ⅔x -1 Same slope Different y-intercept y = ⅔x + 3 y = ⅔x - 1

17. Parent Graph A parent graph is the simplest of the graphs in a family. Let’s summarize how changing the m or b in y = mx + b affects the graph of the equation. Parent: y = x y = x y = 3x As the value of m Increases, the line Gets steeper y = ¼x

18. Parent: y = -x y = -3x y = -x As the value of m Decreases, the line Gets steeper. y = -¼x

19. Parent: y = 2x y = 2x y = 2x - 4 y = 2x + 3 As the value of b Increases, the graph shifts Up on the y-axis. As the value of b decreases, the graph shifts down on the y-axis You can change a graph by changing the slope or y-intercept.

20. Example 4 Change y = -½x + 3 so that the graph of the new equation fits each description. y = -2x + 3 Same y-intercept, steeper negative slope The y-intercept is 3, and the slope is -½. The new equation will also have a y-intercept of 3. In order for the slope to be steeper and still be negative, its value must be less than -½, such as -2. The new equation is y = -2x + 3. y = -½x + 3

21. Example 5 Change y = -½x + 3 so that the graph of the new equation fits each description. y = -½x + 7 Same slope, y-intercept is shifted up 4 units The slope of the new equation will be -½. Since the current y-intercept will be 3 + 4 or 7. The new equation is y = -½x + 7. Always check by graphing y = -½x + 3

22. Your Turn Change y = 2x + 1 so that the graph of the new equation fits each description. Same slope, shifted down 1 unit. y = 2x + 0 Simplified to y = 2x

23. Your Turn Change y = 2x + 1 so that the graph of the new equation fits each description. Same y-intercept, less steep positive slope y = x + 1