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Section 1.4: Angle Measure
Vocab
Vocabulary
Ray
Named by: Two letters
Opposite Rays
Angle
Named By : Three letters
Definition
Ray AB (written as 𝐴𝐵)
consists of the initial point A
and extends in one direction
through point B.
Two rays which have the same endpoint and
extend in opposite directions. If point C is
between A and B, the ray CA (𝐶𝐴) and ray CB
(𝐶𝐵) are opposite rays. This also means that
opposite rays are collinear.
Formed by two rays that have a
common endpoint.
Picture
Vocab
.
Sides
Vertex
The rays of an angle are
called sides.
The vertex is the
common endpoint.
Interior of the Angle
Points that lie on the inside of
an angle. Ex: points S and R
Exterior of the Angle
Points that lie on the outside of
an angle. Ex: points P and O
Example 1
Use the diagram below.
a) Name all angles that have B as a
vertex.
b) Name the sides of angle 5.
c) Write another name for angle 6.
Example 2
a) Name all angles that
have B as a vertex.
b) Name the sides of
Angle 3.
c) What is another name of Angle GHL?
d) Name a point in the interior of Angle DBK.
Vocab
Vocabulary
Right Angle
Definition
An angle that measures
exactly 90◦
Symbol that indicates a 90 degree
angle :
Acute Angle
Obtuse Angle
Congruent Angles
An angle that measures less
than 90◦
An angle that measures
greater than 90◦
Angles that have the exact
same measure.
Symbol that indicates congruent
angles:
Picture
Example 3
Brain Break!
Vocab
Vocabulary
Angle bisector
Definition
A ray that divides an angle
into two congruent angles.
Picture
Example 4
Example 5
𝐾𝑀 bisects JKL. The measures of the two congruent
angles are (8𝑥 − 13)° and (6𝑥 + 11)°. Find the
measures of JKM and MKL.