ANGLES

What is an angle?• Two rays that share the same endpoint

form an angle. • The point where the rays intersect is called

the vertex of the angle.

Ray Vertex

Angle

• Here are some examplesof angles.

Angle Measurements• We measure the size of an angle using

degrees. The symbol for degrees is o

• Here are some examples of angles and their degree measurements.

Acute Angles• An acute angle is an angle measuring

between 0 and 90 degrees. • The following angles are all acute angles.

Obtuse Angles• An obtuse angle is an angle measuring

between 90 and 180 degrees. • The following angles are all obtuse.

Right Angles• A right angle is an angle measuring

exactly 90 degrees. • The following angles are both right angles.

Straight Angle• A straight angle is exactly 180 degrees.

Measuring Angles• You can measure angles using a protractor.

Naming Angles• There are 3 ways to name angles:• Using 3 letters

• Using 1 letter

• Using a number

E

D

F

K

6

< DEFOR

< FEDThe vertex always goes

in the middle

<K

<6

J K

LM

<J OR <MJK OR <KJM <K OR <JKL OR <LKJ

<L OR <MLK OR <KLM<M OR <LMJ OR <JML

PRACTICE TIME!

AcuteAngle

ObtuseAngle

RightAngle

StraightAngle

GREAT JOB!!

Complementary Angles Two Angles are

Complementary if they add up to 90 degrees

(a Right Angle).

These two angles (40° and 50°) are Complementary Angles, because they add up to 90°.

Notice that together they make a right angle.

But the angles don't have to be together.

These two are complementary because 27° + 63° = 90°

Supplementary Angles Two Angles are

Supplementary if they add up to 180 degrees

(straight angle).

These two angles (140° and 40°) are Supplementary

Angles, because they add up to 180°.

Notice that together they make a straight angle.

But the angles don't have to be together.

These two are supplementary because 60° + 120° = 180°

Practice questions out of the textbook:

pg. 418 1-4, 8-11

OL Pg. 422 1-3 (estimate the measure) , 8-14, 20-23, 27-35

PAP Pg. 422 11-33

PAP Pg. 427 13-17, 22-24