WARM UP
Find the reciprocal
1. 2.
3.
4.
Chapter 2
Investigating Geometric Figures
2-3 Parallel and Perpendicular
Lines in the Coordinate Plane
Objective: Graph lines; Recognize
parallel and perpendicular lines by
their slopes
SLOPE
-- steepness of a mountain, grade of a
road, or pitch of a roof
-- vertical change
horizontal change
-- rise
run
=
y2 - y1
x2 - x1
Positive Slope
Negative Slope
Zero Slope
Undefined or NO Slope
Example 1.
What is the slope of this line?
What is the
equation of
this line?
Example 2.
What are the slopes of these lines?
Example 2.
What are the slopes of these lines?
Make a conjecture about
parallel lines and their slopes.
Note:
2 Horizontal lines are always parallel.
2 Vertical lines are always parallel.
Example 3.
What are the slopes of these lines?
Example 4.
What are the slopes of these lines?
Make a conjecture about
perpendicular lines and their
slopes.
Note: **A horizontal line and a vertical
line are always perpendicular to each
other.
**If the slopes are not equal and are not
opposite reciprocals of each other, then
the lines are intersecting lines.
Which of these lines are parallel lines?
1. y = 2x + 1
2. y = 3x + 1
3. y = 2x - 2
4. y = - 1/2x + 1
Which of these lines are perpendicular lines?
1.
2.
3.
4.
y = 2x + 1
y = - 2x - 1
y = - 1/2x + 3
y = 1/2 x - 3
Which of these lines are parallel?
1. x = 4
2. y = - 4
3. x = 2
4. y = 1/4x
Which of these lines are perpendicular to
each other?
1. y = 7
2. y = - 5x - 2
3. x = 7
4. y = 1/5x + 4
Determine if RS and TV are parallel, perpendicular, or neither.
R (­2, 6)
S(3, 4)
Slope Formula
m = y2 - y1
x2 - x1
T (2, 5)
V (0, 0)
Determine if RS and TV are parallel, perpendicular, or neither.
R (5, ­7)
S(­4, ­9)
T (6, 2)
V (­3, 0)
Slope Formula
m = y2 - y1
x2 - x 1
HW # 21
p. 86 # 1, 6­9, 12­19
** Need graph paper
Extra Credit from p. 44 -- Due on Tuesday!