Download Section 1-4

Section 1-4
Angles and their
Measures
Angle
• Formed by two rays with a
common endpoint
–The rays are the sides of the
angle
–The common endpoint is called
the vertex of the angle.
W
X
Y
Name the sides of the Angle.
XY and XW
Name the vertex of the angle. W
When naming an
angle, the vertex
must be in the
middle when using
3 points.
An angle can be
named by its
vertex only if it
names one
angle!
For Example:
W
X
Y
WXY
YXW
X
A
V
D
E
You cannot name this angle by
its vertex because it names 3
angles!
Protractor
• Tool that measures angles
– measured in degrees
Angles that have
the same measure
are called
congruent angles.
Measures are equal!
For example: mABC
 mDEF
Angles are congruent!
For example: ABC
 DEF
An angle separates a plane
in 3 distinct parts:
1. Interior of the angle.
2. Exterior of the
angle.
3. Angle itself.
• A point is in the interior of an
angle if it is between points
that lie on each side of the
angle.
• A point is in the exterior of
an angle if it is not on the
angle or in its interior.
Exterior
W
V
Z
Interior
X
Exterior
Y
Angle Addition
postulate
If P is in the interior of RST,
then mRSP  mPST  mRST
R
S
P
T
Classifying
Angles
Types of angles
1. Right Angle: measure
equals 90 degrees
2. Acute Angle: measure is
greater than 0 degrees and
less than 90 degrees
Types of angles:
3. Obtuse Angle: the measure is
greater than 90 degrees but
less than 180 degrees
4. Straight Angle: measure
equals 180 degrees
Classify each angle.
Right Angle
Obtuse Angle
Acute

Straight Angle
Angle
Adjacent angles:
• Two angles that have a
common vertex and a
common side, but have no
common interior points.