1. Angles of Triangles
Lesson #2
Pg. 19

2. Key Vocabulary Triangle Interior Angle Exterior Angle
A figure formed by three line segments that intersect only at their endpoints
Interior Angle
An angle inside a polygon
Exterior Angle
The angle formed by one side of a triangle and the extension of the adjacent side
Remote Interior Angles
The angles of a triangle that are not adjacent to a given exterior angle

3. Real World Link What is true about the measures of and ?
What kind of angle is formed by , & ?
Write an equation representing the 3 angles
Lines m and n are parallel, Lines p and r are transversals A m 1 3 5 n 2 4 B C p r

4. Sum of the Angles in a Triangle
The sum of the measures of the Interior angles of any triangle is 180°.
Geometers Sketchpad
x + y + z = 180° y° z° x°

5. Example
Find the value of x in the Antigua and Barbuda flag. x°
55°

6. Example
In , if ° and °, what is the ?
Draw a Diagram…

7. Example
The measures of the angles of are in a ratio of 1:4:5, what are the measures of the angles?
Draw a diagram….

8. Example
The measures of the angles of are in a ratio of 2:4:6, what are the measures of the angles?
Draw a diagram….

9. Image Definition (Exterior and Interior Angles)
One interior angle and the exterior angle that share the adjacent side are a “Linear Pair” (180°)
Interior
Exterior

10. Exterior Angles of a Triangle
Interior
Exterior
The measure of an exterior angle of a triangle is equal to the sum of the measures of its two remote interior angles (NOT ADJACENT)

11. Exterior Angles of a Triangle
The measure of an exterior angle of a triangle is equal to the sum of the measures of its two remote interior angles A 1 B C

12. Example
Suppose Find the measure of K 2 1 4 L 5 M

13. Homework
HC: pg (1-15)
REG: pg (1-7, 9, 11, 14, 15)