Measuring AnglesChapter 1 Section 4

ANGLE

An angle is two rays that share a common endpoint.

A

B

C

Angles are named by a point on each side and the common endpoint. To the right is angle ABC.

You can also name an angle by its vertex if it is the only angle with that vertex.

PARTS OF AN ANGLE

SIDE

Vertex

SIDE

TWO REGIONS OF AN ANGLE

Interior

Exterior

CAN YOU NAME AN ANGLE?

J

M

L

K

12

POSTULATE 1-7PROTRACTOR POSTULATE

Every angle can be paired one-to-one with an angle measure on a protractor.

MEASURE

The measure of an angle is the absolute value of the degree paired with each of the rays.

4 TYPES OF ANGLES

Acute angles are less than 90 degrees

Obtuse angles are greater than 90 degrees

Right angles are 90 degrees

Straight angles are 180 degrees

CONGRUENT ANGLES

Congruent angles have the same angle measure.

They may be marked with an arc to show congruence.

POSTULATE 1-8ANGLE ADDITION POSTULATE

If a ray is in the interior of an angle, the two small angles formed can be added together to get the measure of the larger angle.

A

B C

1

2

m 1 m 2

ABCm

ON PAGE 31…

Try problems #1-5 on your own.

Raise your hand when you are finished.