CK-12 Geometry-Concepts

1.6. Angle Classification http://www.ck12.org

The vertex isU. So, the angle can be^6 T UVor^6 V U T. To determine what type of angle it is, compare it to a right
angle. Because it opens wider than a right angle and less than a straight angle it isobtuse.

Example B

What type of angle is 165◦?

165 ◦is greater than 90◦, but less than 180◦, so it isobtuse.

Example C

What type of angle is 84◦?

84 ◦is less than 90◦, so it isacute.

Watch this video for help with the Examples above.

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/52597

CK-12 Foundation: Chapter1AngleClassificationB

Vocabulary

Astraight angleis when an angle measures 180◦. Aright angleis when an angle measures 90◦.Acute anglesare
angles that measure between 0◦and 90◦.Obtuse anglesare angles that measure between 90◦and 180◦. If two lines
intersect to form right angles, the lines areperpendicular.

Guided Practice

Name each type of angle:

1. 90◦


2. 67◦


3. 180◦

Answers:

1. Right