1. EXAMPLE 1
Find slopes of lines in a coordinate plane
Find the slope of line a and line d.
SOLUTION
y2 – y1
x2 – x1 = m =
4 – 2
6 – 8 = 2
– 2
Slope of line a: =
– 1
y2 – y1
x2 – x1 = m =
4 – 0
6 – 6 = 4
Slope of line d:
which is undefined.

2. GUIDED PRACTICE
for Example 1
Use the graph in Example 1. Find the slope of the line.
Line b 2
ANSWER

3. GUIDED PRACTICE
for Example 1
Use the graph in Example 1. Find the slope of the line.
Line c
ANSWER

4. EXAMPLE 2
Identify parallel lines
Find the slope of each line. Which lines are parallel?
SOLUTION
Find the slope of k1 through (– 2, 4) and (– 3, 0). m1 =
0 – 4
– 3 – (– 2 ) =
– 4
– 1 = 4
Find the slope of k2 through (4, 5) and (1, 3). m2
1 – 5
3 – 4 = =
– 4
– 1 = 4

5. EXAMPLE 2
Identify parallel lines
Find the slope of k3 through (6, 3) and (5, – 2). m3
– 2 – 3
5 – 6 = =
– 5
– 1 5
Compare the slopes. Because k1 and k2 have the same slope, they are parallel. The slope of k3 is different, so k3 is not parallel to the other lines.

6. GUIDED PRACTICE
for Example 2
Line m passes through (–1, 3) and (4, 1). Line t passes through (–2, –1) and (3, – 3). Are the two lines parallel? Explain how you know.
Yes; they have the same slope.
ANSWER

7. EXAMPLE 3
Draw a perpendicular line
Line h passes through (3, 0) and (7, 6). Graph the line perpendicular to h that passes through the point (2, 5).
SOLUTION
STEP 1
Find the slope m1 of line h through (3, 0) and (7, 6). m1 =
6 – 0
7 – 3 = 6 4 = 3 2