Download parallel Lines and the Triangle Angle

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.
Triangle Angle-Sum
The sum of the measures of the angles of
a triangle is 180.
m<A + m<B + m<C = 180

C
A
B
Example: Find the missing value

Find m<Z
Z
X 48°
67° Y
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

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
5
2
4
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
Example: Using the Exterior Angle Theorem