1. Equations of Lines Part 2
Students will:
Write slope intercept form given
a point and a slope
Created by: C Garcia

2. b is not given, so we must find it
Example 1
Find the equation of a line (slope-intercept form) passing through point (2, -3) with slope of -5
y = mx + b
b is not given, so we must find it
m is given (-5)
What we Know:
x = 2
y = -3
m = -5
Finding b: y = mx + b
-3 = -5(2) + b
-3 = b
7 = b
Therefore:
y = -5x + 7
Created by: C Garcia

3. b is not given, so we must find it
Example 2
Find the equation of a line (slope-intercept form) passing through point (4, -1) with slope of 7
y = mx + b
m is given (7)
b is not given, so we must find it
What we Know:
x = 4
y = -1
m = 7
Finding b: y = mx + b
-1 = 7(4) + b
-1 = 28 + b
-29 = b
Therefore:
y = 7x – 29
Created by: C Garcia

4. b is not given, so we must find it
Example 3
Find the equation of a line (slope-intercept form) passing through point (-5, -3) with slope of 9
y = mx + b
b is not given, so we must find it
m is given (9)
What we Know:
x = -5
y = -3
m = 9
Finding b: y = mx + b
-3 = 9(-5) + b
-3 = b
42 = b
Therefore:
y = 9x + 42
Created by: C Garcia

5. b is not given, so we must find it
Example 4
Find the equation of a line (slope-intercept form) passing through point (1, -2) with slope of 3
y = mx + b
b is not given, so we must find it
m is given (3)
What we Know:
x = 1
y = -2
m = 3
Finding b: y = mx + b
-2 = 3(1) + b
-2 = 3 + b
-5 = b
Therefore:
y = 3x – 5
Created by: C Garcia

6. Using Point Slope Form
y – y1 = m(x – x1)
Created by: C Garcia

7. Example 5 y – y1 = m(x – x1) Point Slope Form
Find the equation of a line (slope-intercept form) passing through point (1, -2) with slope of 3
y – y1 = m(x – x1) Point Slope Form
y – (-2) = 3(x – 1) Plug in values
y + 2 = 3x – Use distributive Property
y = 3x – 5 Subtract 2
Created by: C Garcia

8. Example 6 y – y1 = m(x – x1) Point Slope Form
Find the equation of a line (slope-intercept form) passing through point (3, 5) with slope of 6
y – y1 = m(x – x1) Point Slope Form
y – 5 = 6(x – 3) Plug in values
y – 5 = 6x – Use distributive Property
y = 6x – Add 5
Created by: C Garcia

9. Example 7 y – y1 = m(x – x1) Point Slope Form
Find the equation of a line (slope-intercept form) passing through point (-3, 5) with slope of -2
y – y1 = m(x – x1) Point Slope Form
y – 5 = -2(x – (-3)) Plug in values
y – 5 = -2(x + 3) Rewrite as
y – 5 = -2x – Use distributive Property
y = -2x – 1 Add 5
Created by: C Garcia

10. Example 8 y – y1 = m(x – x1) Point Slope Form
Find the equation of a line (slope-intercept form) passing through point (7, 8) with slope of -2
y – y1 = m(x – x1) Point Slope Form
y – 8 = -2(x – 7) Plug in values
y – 8 = -2x Use distributive Property
y = -2x Add 8
Created by: C Garcia