Here we can see a few examples of right angles!

Degrees: Measuring Angles

We measure the size of an angle using degrees. Example: Here are some examples of angles and their degree measurements.

ProtractorA device used to measure angles.

Reading a ProtractorDate: 9/8/96 at 22:29:58 From: Bob Vanselow Subject: Reading a Protractor Which side of a protractor scale do you use?

Date: 9/9/96 at 11:39:23 From: Doctor Robert Subject: Re: Reading a Protractor I think that the easiest way to decide which scale to use is to look at the angle you're measuring. If it is greater than a right angle (more than ninety degrees) then use the scale that has numbers greater than 90. If the angle is obviously acute (measures less than 90 degrees), use the scale which has numbersless than 90. Of course you have to line up the protractor correctly with the center point on the vertex of the angle and one of the rays of the anglecoincide with the line on the protractor. Happy measuring! -Doctor Robert, The Math Forum Check out our web site! http://mathforum.org/dr.math/

Acute Angles

An acute angle is an angle measuring between 0 and 90 degrees.

Example:

                                                             

  

Acute Angles are less than 90 degrees.

Even trees have angles!!!

Obtuse Angles

An obtuse angle is an angle measuring between 90 and 180 degrees.

Example:

                                                              

   

Obtuse angles are greater than 90 degrees

Walking around you can find angles!

Right AnglesA right angle is an angle measuring 90 degrees.

Examples:

                                      

Right angles are exactly 90 degrees!!

Sitting on a bench you can find right angles!

RaysAngles can be in relation to rays. A ray is a portion of a line that has one endpoint, while the other goes on forever!

Example:

Rays have just one endpoint, but go the other way forever!!!

Walking from the corner if a sidewalk can represent a ray!!

Straight AnglesStraight angles are exactly 180 degrees. So basically a straight line!

Example:

180°

Straight angles are exactly 180 degrees! Look for a straight line and there is the angle!

The top of a parking garage shows a straight angle!!!

Complementary AnglesTwo angles are called complementary angles if the sum of their degree measurements equals 90 degrees.

Example:

These two angles are complementary.

                                                      

                        

These two angles can be "pasted" together to form a right angle!

                        

Supplementary AnglesTwo angles are called supplementary angles if the sumof their degree measurements equals 180 degrees.

Example:

These two angles are supplementary.

                                                                      

These two angles can be "pasted" together to form a straight line!

                                                

Review

State whether the following are acute, right, or obtuse.1.

2.

3.

4.

5.

??

acute obtuseright

obtuseacute

Complementary and Supplementary

1. Two angles are complementary. One measures 65 degrees.

2. Two angles are supplementary. One measures 140 degrees.

Find the missing angle.

Answer : 25

Answer : 40

Complementary and Supplementary

Find the missing angle. You do not have a protractor.Use the clues in the pictures.

1.2.x

55 165x

X=35 X=15