1. 3-3 Parallel Lines & the Triangle Angle Sum Theorem M11.B.2 2.4.11.B Objectives: 1) To classify triangles and find the measures of their angles. 2) To use exterior angles of triangles.

2. Triangle Angle-Sum The sum of the measures of the angles of a triangle is 180. m<A + m<B + m<C = 180 C B A

3. Example: Find the missing value Find m<Z YX Z 48° 67°

4. Example: Find the missing value Triangle ABC, <ACB is a right angle, and CD AB. Find the values of a, b, and c (Textbook page 133 - TE) T

5. Ex: Find the value of x, y, and z. (textbook page 132) G F J H

6. Classify Triangles: by Angles Equiangular Acute Right Obtuse

7. Classify Triangles: by Sides Equilateral Isosceles Scalene

8. Ex: Classify a Triangle by its Angles & Sides 2 4 5

9. Vocab An exterior angle of a polygon, is an angle formed by a side and an extension of an adjacent side. For each exterior angle of a triangle, the two nonadjacent interior angles are its remote interior angles. Triangle Exterior Angle Theorem. m<1= m<2 + m<3

10. Example: Using the Exterior Angle Theorem