Math 10C
Linear Relations Lesson #3
Parallel & Perpendicular Lines
Objective: By the end of this lesson you will be able to:
- Generalize and apply a rule for determining the slopes of parallel and perpendicular
lines
Investigation 1: Parallel Lines
The line segments shown on the grid are parallel. Find the slope of each in lowest terms.
K
JK:
J
LM:
O
M
NO:
L
N

What can you conclude about the slopes of parallel lines?
Investigation 2: Perpendicular Lines
Perpendicular means that the lines meet at a right angle.
Two sets of perpendicular lines are shown on the grid. Find the slope of the line segments in
each pair. Make sure you write the slopes in lowest terms.
A
AB:
D
C
E
CD:
B
G
EF:
GH:
H

F
How are the slopes of two perpendicular lines related to one another?
Math 10C
Linear Relations Lesson #3
The slopes of parallel lines are ___________.
The slopes of perpendicular lines are ________________ ______________________.
a
i.e. a line with slope
is perpendicular to a line with slope
b
e.g. 1) State the slope of a line that is
a) parallel
b) perpendicular
to the line segment A(-6, 2) B(0, -7).
What is the slope of a line that is perpendicular to a horizontal line?
e.g. 2) Line PQ passes through P(-7, 2) and Q(-2, 10). Line RS passes through R(-3, -4) and S(5,
1). Are the two lines parallel, perpendicular, or neither? Justify your answer.
Math 10C
Linear Relations Lesson #3
e.g. 3) A triangle has vertices A(-4, 2), B(5, 0), and C(-3, -2). Is  ABC a right triangle?
e.g. 4) The line segment joining U(-3, p) and V(-6, 5) is perpendicular to the line segment
joining X(4, 2) and Y(9, 0). Determine the value of p.
Assignment:
p. 349-351 #5, 6, 8-11, 13, 17, 22, 23