Download right angle

Chapter 1
Exploring Geometry:
Points, Lines, and
Angles in the Plane
Section 4
Measuring Angles
Objectives:
Students will be able to use
a protractor to identify and
name angles, and construct
perpendiculars using a
compass.
Measuring Angles
Click here to watch
a video on using a
Protractor to
measure angles.
 Angles are measured in degrees.
 The symbol mA means “the measure of
angle A”.
 A protractor is a device used to find the
measure of an angle.
mA = 65°
Center of the
protractor.
A
Chapter 1
Section 4 - Measuring Angles
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Example 1
Use your protractor to draw an angle that
measures 120°.
mA = 120°
A
Chapter 1
Section 4 - Measuring Angles
3
Types of Angles
 A right angle is an angle whose measure
is 90.
Right angle symbol
 An acute angle is an angle whose
measure is less than 90°.
0° < x < 90°
x°
Chapter 1
Section 4 - Measuring Angles
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Types of Angles
 An obtuse angle is an angle whose
measure is greater than 90° but less than
180°.
90° < x < 180°
x°
 A straight angle is an angle that
measures 180°.
x°
x = 180°
Chapter 1
Section 4 - Measuring Angles
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Perpendicular Lines
 Lines, segments, or rays that form right
angles are perpendicular ().
A
C
D
B
 The symbol  is read “is perpendicular to”.
 AB  CD
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Section 4 - Measuring Angles
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