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Geometry
Section 1.4
What is a Vertex?
The common
endpoint of the
two rays that
form an angle.
The tool we use to measure an angle is
called?
Protractor
Postulate #3
• The Protractor Postulate:
• A ray and a point not on that ray can be
connected to form an angle with a measure
between 0 and 180 degrees.
An angle that measures between
90 degrees and 180 degrees is
called what?
Angle Classifications
• Straight angles measure either 0 degrees or 180
degrees
• Acute Angles measure larger than 0 degrees but
smaller than 180 degrees
• Right Angles measure exactly 90 degrees
• Obtuse Angles measure larger than 90 degrees but
smaller than 180 degrees.
Postulate #4
• Angle Addition Postulate
• m ABC = m ABD + m DBC
A
D
B
C
What is an Angle Bisector?
An angle
bisector is a ray
that splits an
angle into two
congruent
angles.