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Degrees and Protractor

Degrees are the unit of measure used for angles, just as feet are used to measure distance. The symbol for degrees is "°". There are 360° in a full circle, and 90° in a right angle. A protractor is used for measuring angles. As shown below, a protractor is a half or full circle measuring device, marked in degrees along the outer edge, with a straight line running from 0° to 180°. There is a small hole in the center of the protractor. To use a protractor:

  1. Place the hole of the protractor over the point of the angle where the lines meet.
  2. Make sure one side of the angle is on the zero line.
  3. Read the degrees off the protractor where the line of the other side is or mark a point along the edge at the appropriate angle measurement.


Example 1 - Part A. Measure angles 1, 2, and 3 using a protractor to follow the steps above.



You should find that the angles measure as follows:



Part B. What is the sum of angles 1 and 2? How does that number compare to angle 3?

The sum of angles 1 and 2 is 180 degrees. Angle 3 also equals 180 degrees. Angle 3 is a straight line, so it follows that the sum of angles 1 and 2, 180°, is also a straight line.

Part C. Add angles 1, 2, and 3. The sum of angles 1, 2, and 3 equals 360 degrees.

There are 360 degrees in a circle and angles 1, 2, and 3 together complete the circle.