Download Angle Sum Theorem WS pg. 189

NAME ______________________________________________ DATE
4-2
____________ PERIOD _____
Study Guide and Intervention
Angles of Triangles
Angle Sum Theorem
If the measures of two angles of a triangle are known,
the measure of the third angle can always be found.
Angle Sum
Theorem
The sum of the measures of the angles of a triangle is 180.
In the figure at the right, m/A 1 m/B 1 m/C 5 180.
B
A
Example 1
Example 2
Find the missing
angle measures.
Find m/T.
S
B
358
908
T
m/R 1 m/S 1 m/T 5 180
25 1 35 1 m/T 5 180
60 1 m/T 5 180
m/T 5 120
Angle Sum
Theorem
A
588
C
1
2
D
3
1088
E
Substitution
Add.
Subtract 60
from each side.
m/1 1 m/A 1 m/B
m/1 1 58 1 90
m/1 1 148
m/1
5
5
5
5
180
180
180
32
m/2 5 32
m/3 1 m/2 1 m/E
m/3 1 32 1 108
m/3 1 140
m/3
5
5
5
5
180
180
180
40
Angle Sum Theorem
Substitution
Add.
Subtract 148 from
each side.
Vertical angles are
congruent.
Angle Sum Theorem
Substitution
Add.
Subtract 140 from
each side.
Exercises
Find the measure of each numbered angle.
1.
2.
M
S
628
908
1
P
1
3. V
W
5.
R
4. M
608
U
308
Q
N
3
668
1
308
1
T
588
2
Q
N
2
508
O
P
6. A
R
208
1 2
1528
T 608
W
©
308
Glencoe/McGraw-Hill
G
S
189
1
D
Glencoe Geometry
Lesson 4-2
258
R
C