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Angle Measure
Degree – A unit of measure resulting from the
division of the circumference of a circle into
360 parts.
Ray – A part of a line that has one endpoint
and extends infinitely in one direction.
Rays are named by stating the endpoint first
and then any other point on the ray. Rays
are labeled using a one-directional arrow.
Angle Measure
Opposite Rays – Two rays determined by
choosing a point on a line. Thus, these rays
share a common endpoint and are collinear.
Angle – A geometric figure formed by two
noncollinear rays that have the same
endpoint.
Sides – The rays that form the angle.
Vertex – The common endpoint.
Angle Measure
Naming an Angle – An angle is named using
either its vertex, its vertex and a point on
each ray, or a numerical label.
Labeling an Angle – When labeling an angle,
use the  symbol in front of the angle’s
name. When mentioning an angle’s
measure, use an m in front of the  to
indicate measure.
a. Name all angles that have X as a vertex.
Answer: 1, 2, 3, and RXB
or RXN
b. Name the sides of 3.
Answer:
c. Write another name for 3.
Answer: AXB, AXN, NXA, BXA
Angle Measure
Interior of an angle – A point is in the
interior of an angle if it does not lie on the
angle itself and it lies on a segment with
endpoints that are on the sides of the angle.
Exterior of an angle – A point is in the
exterior of an angle if it is neither on the
angle itself nor in the interior of the angle.
Angle Measure
Acute angle - An angle is acute if and only if
its measure is between 0 and 90 degrees.
Right angle - An angle is a right angle if and
only if its measure equals 90 degrees.
Obtuse angle - An angle is obtuse if and only
if its measure is more than 90 degrees and
less than 180 degrees.
Measure each angle named and classify
it as right, acute, or obtuse.
a. CZD
Answer: 150, obtuse
b. CZE
Answer: 90, right
c. DZX
Answer: 30, acute
Angle Measure
Congruent Angles – Angles that have the
same measure.
Angle Bisector – A ray that divides an angle
into two congruent angles.