1. 4.1 Triangle Sum Theorem October 10, 2012
Chapter 4: Congruent Triangles
Activity: Find the sum of the measures of the angles.
Materials: Paper, Ruler & Scissors
Draw 2 different sized triangles with one of the sides extended.
Label the 4 angles. Cut out the triangles.
A
W
X Y Z
B C D
1st Triangle: Tear off the three corners. Place them next to each
other on the extended line.
Make a conjecture about the sum of the measures of interior <s
2nd Triangle: Tear off corners that aren't next to the exterior <s.
Use them to fill the exterior <.
Make a conjecture about the relationship between the measure of
an exterior < and the nonadjacent interior <s.
Conclusions:
The sum of the measures of the interior <s of a triangle = 180.
The measure of the exterior angle of a triangle the sum of the 2
nonadjacent interior <s.
Oct 15­1:24 PM
HW pg. 221 #8­18 evens, 21­26, 32 & 36 1

2. 4.1 Triangle Sum Theorem October 10, 2012
4­1 Triangle Sum Properties
Objectives:
To understand the sum of the measures of the angles of a
triangle.
Classify Triangles by Sides
Scalene Isosceles Equilateral
Classify Triangles by Angles
Acute Right Obtuse Equiangular
Oct 15­1:30 PM
HW pg. 221 #8­18 evens, 21­26, 32 & 36 2

3. 4.1 Triangle Sum Theorem October 10, 2012
Triangle Sum Theorem
The sum of the measures of the angles in every triangle is _____.
xo x = ______
54o 39o
no n = ______
135o 30o
Oct 17­9:52 AM
HW pg. 221 #8­18 evens, 21­26, 32 & 36 3

4. 4.1 Triangle Sum Theorem October 10, 2012
Exterior Angle Theorem
The measure of an exterior < of a triangle = the sum of the measures of the 2
nonadjacent interior <s.
Nonadjacent
Interior
Exterior Angles
Angle
2
1 3
Corollary to the Triangle Sum Theorem
The acute angles of a right triangle are complementary.
A
<A + <C = 90
B C
Sep 20­12:46 PM
HW pg. 221 #8­18 evens, 21­26, 32 & 36 4

5. 4.1 Triangle Sum Theorem October 10, 2012
Find the measure of each numbered angle in the figure.
3
2
50o 1 120 o 4 5
78 o 56o
109o
95o
1
2 3
33 o 24o
Sep 20­12:53 PM
HW pg. 221 #8­18 evens, 21­26, 32 & 36 5

6. 4.1 Triangle Sum Theorem October 10, 2012
HW
pg. 221
#8­18 evens,
21­26, 32 & 36
Oct 13­7:13 AM
HW pg. 221 #8­18 evens, 21­26, 32 & 36 6