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 ( )x

Rule: 0 180x

x

4

Rulers

5

A Protractor

Classifying Angles by their Measures

Acute Right Obtuse

x°

x < 90°

x°

x = 90°

x°

x > 90°

Straight 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 is a straight angle, find and

KLMm KLN m NLM

• How many s can you find? Name them.

A B

CD

1 2

•3 s–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.

Definition: Congruent Segments have equal length

Definition: Congruent Angles have equal measure

Congruence Symbol:

Meaning: If thenMeaning: If then

1 2 1 2m m AB CD AB CD

Identify the line segments that are congruent in the figure.

Using Marks to Identify Congruent Line Segments

A B

DC

E FAB CD

AC BD

BF DF EC AE

One tick mark

Two tick marks

Three tick marks

Course 2

Building Bocks of Geometry

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 = 60 minutes

1 minute = 60 seconds

1 60" 1' '60