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  1. 1. Degrees: Measuring AnglesWe measure the size of an angle using degrees.Example: Here are some examples of angles and their degree measurements.
  2. 2. A device used to measure angles.
  3. 3. Reading a ProtractorDate: 9/8/96 at 22:29:58 From: Bob VanselowSubject: Reading a Protractor Which side of aprotractor scale do you use?Date: 9/9/96 at 11:39:23 From: Doctor RobertSubject: Re: Reading a ProtractorI think that the easiest way to decide which scale to use is to look at the angleyoure measuring. If it is greater than a right angle (more than ninety degreesthen use the scale that has numbers greater than 90. If the angle is obviouslyacute (measures less than 90 degrees), use the scale which has numbersless than 90. Of course you have to line up the protractor correctly withthe 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!
  4. 4. An acute angle is an angle measuring between 0and 90 degrees.Example:
  5. 5. Obtuse AnglesAn obtuse angle is an angle measuring between 90 and180 degrees.Example:
  6. 6. A right angle is an angle measuring 90 degrees.Examples:
  7. 7. Two angles are called complementary angles if thesum of their degree measurements equals 90 degrees.Example:These two angles are complementary.
  8. 8. These two angles can be "pasted"together to form a right angle!
  9. 9. Supplementary AnglesTwo angles are called supplementary angles if the sumof their degree measurements equals 180 degrees.Example:These two angles are supplementary.
  10. 10. These two angles can be"pasted" together to forma straight line!
  11. 11. Vertical AnglesFor 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 degreemeasurement.
  12. 12. Review State whether the following are acute, right, or obtuse.1. 3. 5. acute obtuse right2. 4. acute ? ? obtuse
  13. 13. Complementary and Supplementary Find the missing angle.1. Two angles are complementary. One measures 65 degrees. Answer : 252. Two angles are supplementary. One measures 140 degrees. Answer : 40
  14. 14. Complementary andSupplementaryFind the missing angle. You do not have a protractor.Use the clues in the pictures. 1. x 2. 55 x 165 X=35 X=15
  15. 15. Vertical Angles Find the missing angle. You do not have a protractor. Use the clues in the pictures. X=58 x 58
  16. 16. More drawings F E 20 90 70 D G C 70 90 J 20 H
  17. 17. Final Drawing B C 68 52 60 A G D 60 52 68 F E