 |
|
 |
|
 |
 |
|
|
|
|
Key
Idea
A number can be
used to describe
the size of an
angle’s opening. |
|
| |
Vocabulary
• angle
• vertex
• sides
• interior
• exterior
• degrees
• protractor
• acute angle
• right angle
• obtuse angle
• straight angle |
|
| |
Materials
• ruler or
straightedge
• protractor |
|
|
Measuring and
Classifying Angles |
 |
|
 |
|
| How can you measure angles? |
|
An angle is formed by two rays
that have the same endpoint. The
common endpoint is called the
vertex
(plural: vertices). The rays
are the
sides of the angle.
|
|
Angle
RST
is shown at the right. We write this
as  .
It can also be named 
or just  .
When three letters are used, the middle
letter names the vertex. The interior
and exterior
of the angle are also shown. |
|
There are various ways to
measure an angle’s opening.
For example, if we measure it in
“wedges,” we could say that the
measure of  is 4 wedges.
|
|
|
|
 |
|
 |
|
 |
|
 |
|
In math, we usually measure
angles in degrees (°). One
degree is a very skinny wedge. It
takes 90 degrees, written 90°, to
fill a square corner. The measure
of  is 90°. |
 |
|
 |
|
 |
|
|
|
|
|
|
|