CK-12 Geometry Concepts

1.5. Angle Measurement http://www.ck12.org

Using the Angle Addition Postulate,m^6 QRT= 15 ◦+ 30 ◦= 45 ◦.

Example D

Draw a 135◦angle.

Following the steps from above, your angle should look like this:

Watch this video for help with the Examples above.

MEDIA

Click image to the left for more content.

CK-12 Foundation: Chapter1MeasuringAnglesB

Vocabulary

Aprotractoris a measuring device that measures how “open” an angle is. Angles are measured indegrees, and
labeled with a◦symbol. Acompassis a tool used to draw circles and arcs.

Guided Practice

1. Use a protractor to measure^6 RSTbelow.


2. What ism^6 LMNifm^6 LMO= 85 ◦andm^6 NMO= 53 ◦?


3. Ifm^6 ABD= 100 ◦, findxandm^6 ABCandm^6 CBD?

Answers:

1. The easiest way to measure any angle is to line one side up with 0◦. This angle measures 100◦.


2. From the Angle Addition Postulate,m^6 LMO=m^6 NMO+m^6 LMN. Substituting in what we know, 85◦=
   53 ◦+m^6 LMN, so 85◦− 53 ◦=m^6 LMNorm^6 LMN= 32 ◦.


3. From the Angle Addition Postulate,m^6 ABD=m^6 ABC+m^6 CBD. Substitute in what you know and solve the
   equation.

100 ◦= ( 4 x+ 2 )◦+( 3 x− 7 )◦

100 ◦= 7 x− 5 ◦

105 ◦= 7 x

15 ◦=x

So,m^6 ABC= 4 ( 15 ◦)+ 2 ◦= 62 ◦andm^6 CBD= 3 ( 15 ◦)− 7 ◦= 38 ◦.

Practice

1. What ism^6 LMNifm^6 LMO= 85 ◦andm^6 NMO= 53 ◦?


2. Ifm^6 ABD= 100 ◦, findx.