8/9/2009
MEASURE OF AN ANGLE
The measure of an angle is the degrees from the initial side ray to the
terminal side ray. We can measure an angle in degrees or in radians.
If we look at a circle, we can better understand degrees. A circle has
360 degrees. A straight line is 180 degrees. When you want to
indicate measure of an angle, use the symbol m < ABC = 45 degrees.
135
degrees
POOL ROOM MATH
Lesson 2.2
90
degrees
45
degrees
0
degrees
180
degrees
225 degrees
270
degrees
PROTRACTOR
We use the protractor to measure the number
of degrees in an angle.
Step 1: Place the center mark of the protractor
on the vertex of the angle.
Step 2: Rotate the zero-edge of the protractor to
line up with one side of the angle.
Step 3: Read the measure of the angle where
the other side of the angle crosses the
protractor’s scale.
335
degrees
USING THE RIGHT SCALE
Note whether the angler you are measuring
looks like it’s measure is greater than or less
than 90 degrees.
If the angle looks less than 90 degrees, use the
smaller of the two numbers on the protractor.
If the angle looks greater than 90 degree4s, use
the larger of the two numbers on the protractor.
1
8/9/2009
CONGRUENT
CONGRUENT ANGLES AND SEGMENTS
Two figures that have the EXACT same size and shape are
called congruent figures. For two segments or angles to be
congruent, they would have to have the same measure.
To indicate that they are congruent, we use tick marks that are
the same.
Two angles are congruent angles, if and only if
they have the same measure
Two segments are congruent segments, if and
only if they have the same measure.
The symbol for congruent is

2