3-3 Parallel Lines & the Triangle Angle Sum TheoremM11.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.

Triangle Angle-SumThe sum of the measures of the

angles of a triangle is 180. m<A + m<B + m<C = 180

C

BA

Example: Find the missing valueFind m<Z

YX

Z

48° 67°

Example: Find the missing valueTriangle ABC, <ACB is a right

angle, and CD AB. Find the values of a, b, and c (Textbook page 133 - TE)

T

Ex: Find the value of x, y, and z.(textbook page 132)

G

F J H

Classify Triangles: by Angles

Equiangular

Acute

Right

Obtuse

Classify Triangles: by Sides

Equilateral

Isosceles

Scalene

Ex: Classify a Triangle by its Angles & Sides

2

45

VocabAn 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

Example: Using the Exterior Angle Theorem