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Chapter 13
L13-1 Notes:
Angles
Vocabulary
 Angles have two sides that share a common
endpoint called the vertex of the angle.
Vocabulary
 The most common unit of measure for angles
is the degree. A circle can be separated into
360 equal-sized parts.
Types of Angles
right angle exactly 90°
acute angle less than 90°
obtuse angle greater than 90°
straight angle exactly 180°
Measure Angles
Use a protractor to find the measure of each angle. Then classify
each angle as acute, obtuse, right, or straight.
1.
Measure Angles
Use a protractor to find the measure of each angle. Then classify
each angle as acute, obtuse, right, or straight.
2.
Pairs of Angles
 Two angles whose sum is 90º are complementary angles.
Pairs of Angles
 Two angles whose sum is 180º are supplementary angles.
Find the Missing Measure
Chapter 13
L13-2 Notes:
Using Angle Measures
Estimating Measures
To estimate the measure of an angle, compare
it to an angle whose measure you know.
1. Estimate the measure of the angle shown.
Compare the given angle to an angle whose
measure you know. The angle is a little less
than a 90° angle. So, a reasonable estimate is
about 80°.
On Your Own…
Estimate the measure of each angle.
1.
2.
Draw an Angle
Draw a 74⁰ angle.
Step 1 Draw one side of the angle.
Then mark the vertex and draw an
arrow.
Step 2 Place the center point of the
protractor on the vertex. Align the
mark labeled 0 on the protractor
with the line. Find 74° on the
correct scale and make a pencil
mark.
Step 3 Use a straightedge to draw
the side that connects the vertex
and the pencil mark.
On Your Own…
Use a protractor and a straightedge to draw
angles having the following measurements.
1. 68⁰
2. 105⁰
Chapter 13
L13-3 Notes:
Bisectors
Vocabulary
 To bisect something means to separate it
into two equal parts.
 Lines with the same measure are congruent.
 Two line segments are perpendicular if they
meet at right angles.
Bisect a Line Segment
 Draw a line segment measuring 6 inches.
Then use a straightedge to bisect the
segment.
 Draw a 120° angle. Then use a straightedge
and a protractor to bisect the angle.
On Your Own…
Draw each line segment or angle having the
given measurement. Then use a straightedge
and a protractor to bisect the line segment or
angle.
1. 3 cm
2. 85º