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Angle Measurements

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**Degrees: Measuring Angles**

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

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Protractor A device used to measure angles.

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**Date: 9/9/96 at 11:39:23 From: Doctor Robert **

Reading a Protractor Date: 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 numbers less 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 angle coincide with the line on the protractor. Happy measuring! -Doctor Robert, The Math Forum Check out our web site!

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Acute Angles An acute angle is an angle measuring between 0 and 90 degrees. Example:

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** Obtuse Angles Example:**

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

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Right Angles A right angle is an angle measuring 90 degrees. Examples:

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**These two angles are complementary. **

Complementary Angles Two angles are called complementary angles if the sum of their degree measurements equals 90 degrees. Example: These two angles are complementary.

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

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**These two angles are supplementary. **

Supplementary Angles Two angles are called supplementary angles if the sum of their degree measurements equals 180 degrees. Example: These two angles are supplementary.

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

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Vertical Angles For any two lines that meet, such as in the diagram below, angle AEB and angle DEC are called vertical angles. Angle BEC and angle AED are also vertical angles. Vertical angles have the same degree measurement. 110 70 70 110

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**Review State whether the following are acute, right, or obtuse. 1. 3.**

5. acute obtuse right 2. 4. ? acute obtuse ?

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**Complementary and Supplementary**

Find the missing angle. 1. Two angles are complementary. One measures 65 degrees. 2. Two angles are supplementary. One measures 140 degrees. Answer : 25 Answer : 40

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**Complementary and Supplementary**

Find the missing angle. You do not have a protractor. Use the clues in the pictures. 2. 1. x x 55 165 X=35 X=15

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**Vertical Angles Find the missing angle. You do not have a protractor.**

Use the clues in the pictures. X=58 x 58

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More drawings F E 20 90 70 D G C 70 90 J 20 H

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Final Drawing B C 68 60 52 A G D 60 52 68 F E

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Chapter 1 Basics of Geometry

Chapter 1 Basics of Geometry

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