Download 1.2 Measurements of Segments and Angles

Geometry1.2
Measurements of
Segments and
Angles
1.2 Measurements of
Segments and Angles
•A geometric object is distinct from
its measure. Symbols are used
carefully to distinguish between…
Object Name
Symbol
Measure
Linear Units: meters (m), centimeters
(cm), feet (ft), miles (mi)
Angle Units: degrees (
Rule:
)x
0  x  180
x
Rulers
4
A Protractor
5
Classifying Angles by their Measures
Acute 
x°
x < 90°
Straight 
Right 
Obtuse 
x°
x°
x = 90°
x > 90°
x°
x = 180°
Types of Angles
• Acute Angle:
Measures between
0° and 90°
• Right Angle:
Measure of 90°
• Obtuse Angle:
Measure between
90° and 180°
• Straight Angle:
Measure of 180°
Example
Given that KLMis a straight angle, find
mNLM
and
mKLN
• How many s can you find? Name them.
B
A
•3 s
1 2
D
–ADB or BDA
–BDC or CDB
–ADC or CDA
•Notice D (the vertex) is always in the middle.
•Can’t use D
•But 1 or 2 could be added.
C
Definition: Congruent Segments
have equal length
Definition: Congruent Angles have
equal measure
Congruence Symbol:

Meaning: If 1  2 then
Meaning: If AB  CDthen
m1  m2
AB  CD
Building Bocks of Geometry
Using Marks to Identify Congruent Line Segments
Identify the line segments that are congruent in the figure.
A
AB  CD
One tick mark
AC  BD
Two tick marks
E
BF  DF  EC  AE Three tick marks
Course 2
B
F
C
D
Using Marks to Identify Congruent
Angles and Segments
Name the Congruent Objects
Name the Congruent Objects
Alternative Method for Measuring
Angles
DMS:
Degrees , Minutes , Seconds
 
 
1 degree 1 = 60 minutes 60
'
1 minute 1'= 60 seconds  60"