1. You found the slopes of lines.
Write an equation of a line given information about the graph.
Solve problems by writing equations.
Then/Now

2. slope-intercept form
point-slope form
Vocabulary

3. Concept

4. y = mx + b Slope-intercept form y = 6x + (–3) m = 6, b = –3
Slope and y-intercept
Write an equation in slope-intercept form of the line with slope of 6 and y-intercept of –3. Then graph the line.
y = mx + b Slope-intercept form
y = 6x + (–3) m = 6, b = –3
y = 6x – Simplify.
Example 1

5. Plot a point at the y-intercept, –3.
Slope and y-intercept
Answer:
Plot a point at the y-intercept, –3.
Use the slope of 6 or to find another point 6 units up and 1 unit right of the y-intercept.
Draw a line through these two points.
Example 1

6. Write an equation in slope-intercept form of the line with slope of –1 and y-intercept of 4.
A. x + y = 4
B. y = x – 4
C. y = –x – 4
D. y = –x + 4
Example 1

7. Slope and a Point on the Line
Write an equation in point-slope form of the line whose slope is that contains (–10, 8). Then graph the line.
Point-slope form
Simplify.
Example 2

8. Graph the given point (–10, 8).
Slope and a Point on the Line
Answer:
Graph the given point (–10, 8).
Use the slope to find another point 3 units down and 5 units to the right.
Draw a line through these two points.
Example 2

9. Write an equation in point-slope form of the line whose slope is that contains (6, –3).B. C. D.
Example 2

10. Step 1 First, find the slope of the line.
Two Points
A. Write an equation in slope-intercept form for a line containing (4, 9) and (–2, 0).
Step 1 First, find the slope of the line.
Slope formula
x1 = 4, x2 = –2, y1 = 9, y2 = 0
Simplify.
Example 3

11. Distributive Property
Two Points
Step 2 Now use the point-slope form and either point to write an equation.
Point-slope form
Using (4, 9):
Distributive Property
Add 9 to each side.
Answer:
Example 3

12. Step 1 First, find the slope of the line.
Two Points
B. Write an equation in slope-intercept form for a line containing (–3, –7) and (–1, 3).
Step 1 First, find the slope of the line.
Slope formula
x1 = –3, x2 = –1, y1 = –7, y2 = 3
Simplify.
Example 3

13. Distributive Property
Two Points
Step 2 Now use the point-slope form and either point to write an equation.
Point-slope form
Using (–1, 3):
m = 5, (x1, y1) = (–1, 3)
Distributive Property
Add 3 to each side.
y = 5x + 8
Answer:
Example 3

14. A. Write an equation in slope-intercept form for a line containing (3, 2) and (6, 8).B. C. D.
Example 3a

15. B. Write an equation in slope-intercept form for a line containing (1, 1) and (4, 10).
A. y = 2x – 3
B. y = 2x + 1
C. y = 3x – 2
D. y = 3x + 1
Example 3b

16. This is a horizontal line.
Write an equation of the line through (5, –2) and (0, –2) in slope-intercept form.
Step 1
Slope formula
This is a horizontal line.
Example 4

17. Subtract 2 from each side. y = –2
Horizontal Line
Step 2
Point-Slope form
m = 0, (x1, y1) = (5, –2)
Simplify.
Subtract 2 from each side.
y = –2
Answer:
Example 4

18. Write an equation of the line through (–3, 6) and (9, –2) in slope-intercept form.B. C. D.
Example 4

19. Concept

20. y = mx + b Slope-Intercept form 0 = –5(2) + b m = –5, (x, y) = (2, 0)
Write Equations of Parallel or Perpendicular Lines
y = mx + b Slope-Intercept form
0 = –5(2) + b m = –5, (x, y) = (2, 0)
0 = –10 + b Simplify.
10 = b Add 10 to each side.
Answer: So, the equation is y = –5x + 10.
Example 5

21. A. y = 3x
B. y = 3x + 8
C. y = –3x + 8 D.
Example 5