1. SLOPE-INTERCEPT FORM LINEAR FUNCTIONS

2. y = mx + b Slope - measure of the steepness of a line y-intercept - where the line crosses the y-axis

3. First let’s practice with the slope.

4. 4 5 This line has a slope of 4/5. It shows a rise of 4 and a run of 5. Slope = rise run

5. This line has a slope of 4/5. Or use the formula: m = (2,1) (-3,-3)

6. -6 5 Note this line has a negative slope. m = - 5 / 6

7. positive slopenegative slope

8. No slopeSlope is 0

9. Now you tell what kind of slope each of the following lines have. Click the mouse to check your answer. positive

11. No slope

12. negative

13. zero

14. negative

15. positive

16. negative

17. Now let’s look at the y-intercept.

18. This line intercepts the y-axis at 2 so in the slope intercept form, the b = 2.

19. Name the y-intercept. Click to check b = -3

20. b = 2

21. b = 3.5

22. b = 0

23. Now let’s combine the slope and the y-intercept to write the equation of the line shown.

24. -6 3 m = 3 /- 6 or m = -.5 b = 1 y = mx + b y = -.5x + 1

25. 6 3 m = 6 / 3 or m = 2 y = 0 y = mx + b y = 2x + 0 y = 2x

26. m = 0 b = - 2 y = mx + b y = 0x + (-2) y = -2

27. No slope No y-intercept x = -1 Special case:

28. x = 3

29. Your turn. Click mouse to check

30. y = 3x + 1

31. y = 3x

32. y = - 1/3 x - 1

33. x = -3

34. y = -4/3 x

35. y = 4

36. But what do you do if the y-intercept is not a whole number? (3,-4) (-3,1)

37. Use any 2 points on the line to find the slope. (3,-4) (-3,1) Then use that slope and either of the 2 points to find the y- intercept.

38. (3,-4) (-3,1) m = -5/6 b = -1 1/2 y= mx + b y = -5/6x - 1 1/2

39. Try the next one…

40. y = 4x - 8

41. When you have the equation of the line, any point on the line will make the equation a true statement. This is a good way to check your equation.