1. Chapter 1: Essentials of Geometry
Section 1.4: Measure and Classify Angles

2. Section 1.4: Measure and Classify Angles
Goal: Measure and classify angles. Add angle measures.

3. Section 1.4: Measure and Classify Angles
An angle is the figure formed by two rays that have the same endpoint. The two rays are called the sides of the angle, and their common endpoint is the vertex of the angle.
side
vertex
side

4. Section 1.4: Measure and Classify Angles
Naming the angle: A 1 B C R S 2 3 E T

5. Section 1.4: Measure and Classify Angles
Acute angle: measure between o and 90 degrees (non inclusive) Right angle: measure of 90° Obtuse angle: measure between 90 and 180 degrees (non inclusive) Straight angle: measure of 180°

6. Section 1.4: Measure and Classify Angles
Angle Addition Postulate If P is in the interior of <RST, then the measure of <RST is the sum of the measures of <RSP and <PST. m <RSP + m <PST = m <RST R P S T

7. Section 1.4: Measure and Classify Angles
Congruent Angles: angles that have the same measure m <R = m < S or < R ≅ < S

8. Section 1.4: Measure and Classify Angles
Using a Protractor: Handout

9. Section 1.4: Measure and Classify Angles
Bisector of an angle: the ray that divides the angle into two congruent angles If YW is the angle bisector, how are the above angles related? X Y W Z

10. Section 1.4: Measure and Classify Angles
Try together: Pg (all) Homework: Pg. 28 #8-42 (even)