3-7 Perpendicular Lines
Lines that intersect at an angle of 90 degrees are perpendicular lines.
For example, let’s say that we have the
line AB and the line CD
Now, if the
lines intersect
at an angle of
C
90o,
A
D
then AB  CD.
B
Perpendicular lines are lines
that intersect to form a right angle.
m
Definition of
Perpendicular
Lines
Symbols: m  n
n
m
1 2
4 3
n
If two lines are perpendicular,
then they form 4 right angles.
a
Theorem 3-8
1
2
4
3
Symbols: a  b
b
In the figure, OP  MN and NP  QS.
Determine whether each of the
following is true or false.
1
False. Since OP  MN,
2
P
M
1
5
2 R 6
Q
True.
are vertical angles, and vertical
angles are congruent.
3
7
O
True. If two lines are perpendicular,
then they form 4 right angles.
4 QR  PR
False.
8 3
S 4
N