1. Chapter 1 Exploring Geometry: Points, Lines, and Angles in the Plane Section 4 Measuring Angles Objectives: Students will be able to use a protractor to identify and name angles, and construct perpendiculars using a compass.

2. Chapter 1Section 4 - Measuring Angles2  Angles are measured in degrees.  The symbol m  A means “the measure of angle A”.  A protractor is a device used to find the measure of an angle. Measuring Angles Center of the protractor. A m  A = 65° Click here to watch a video on using a Protractor to measure angles.

3. Chapter 1Section 4 - Measuring Angles3 Example 1 Use your protractor to draw an angle that measures 120°. A m  A = 120°

4. Chapter 1Section 4 - Measuring Angles4  A right angle is an angle whose measure is 90 .  An acute angle is an angle whose measure is less than 90°. Types of Angles Right angle symbol 0° < x < 90° x°x°

5. Chapter 1Section 4 - Measuring Angles5  An obtuse angle is an angle whose measure is greater than 90° but less than 180°.  A straight angle is an angle that measures 180°. Types of Angles 90° < x < 180° x°x° x°x° x = 180°

6. Chapter 1Section 4 - Measuring Angles6 Perpendicular Lines  Lines, segments, or rays that form right angles are perpendicular (  ).  The symbol  is read “is perpendicular to”.  AB  CD A C B D