1. Writing the Equation of a Line from a Graph

2. Two equations we can use…
The slope-intercept form of a linear equation is
y = mx + b.
m represents the slope
b represents the y-intercept
We can use this equation when we can accurately read the y-intercept from the graph

3. Two equations we can use…
The point-slope form of a linear equation is
y – y1 = m(x – x1)
m represents the slope
(x1, y1) represents a point
We can use this equation when we cannot accurately read the y-intercept from the graph

4. Example 1
y = mx + b
b = -3
m =
y = x - 3 x y +2 +3

5. Example 2
y = mx + b
b = 1
m =
y = x + 1 x y -2 +1

6. Example 3
y = mx + b
b = 4
m = 0
y = 0x + 4, y = 4 x y

7. Example 4 x y
There is no b
m = undefined
x = -3

8. Example 5 m = The y-intercept cannot be read off accurately
If you are not sure about the y-intercept use this method
Read any two points off
m = x y
(-2,4)
(2,-3)

9. Example 5 continued Points (-2, 4) and (2, -3) Slope: m =
Use slope and one point with
y – y1 = m(x – x1) x y

10. Remember
Parallel lines have the same slope and different y-intercepts.
Perpendicular lines have slopes that are opposite reciprocals.

11. Homework
Find the linear inequalities for each colored region in the provided design