9.2 Parallel and Perpendicular Lines 725WRITING
- PHRASES Explain what you think each of these
phrases means. How is geometry involved?
a. The president did a complete 180-degree flip on
the subject of a tax cut.
b. The rollerblader did a “360” as she jumped off
the ramp. - In the statements below, the ° symbol is used in two
different ways. Explain the difference.
and 85°F - Can two angles that are complementary be equal?
Explain. - Explain why the angles highlighted below are not
vertical angles.
m(A)85°REVIEW
- Add:
- Subtract:
- Multiply:
- Divide:
12
17
4
34
5
8
2
15
6
5
3
4
1
8
1
2
1
2
2
3
3
4
SECTION 9.2
Parallel and Perpendicular Lines
In this section, we will consider parallel and perpendicularlines. Since parallel lines are
always the same distance apart, the railroad tracks shown in figure (a) illustrate one
application of parallel lines. Figure (b) shows one of the events of men’s gymnastics,
the parallel bars. Since perpendicular lines meet and form right angles, the monument
and the ground shown in figure (c) illustrate one application of perpendicular lines.
Objectives
1 Identify and define parallel and
perpendicular lines.
2 Identify corresponding angles,
interior angles, and alternate
interior angles.
3 Use properties of parallel lines
cut by a transversal to find
unknown angle measures.1 Identify and define parallel and perpendicular lines.
If two lines lie in the same plane, they are called coplanar.Two coplanar lines that do
not intersect are called parallel lines.See figure (a) on the next page. If two lines
do not lie in the same plane, they are called noncoplanar. Two noncoplanar lines that
do not intersect are called skew lines.
The symbol indicates
a right angle.(a) (b) (c)