Transcript 3-3 Parallel Lines and the Triangle Sum Theorem

L.E.Q. How do you find measures of interior
and exterior angles of triangles?




Draw and cut out a large triangle.
Number the angles and tear them off.
Place the three angles adjacent to each other
to form one angle.
What do you see?
65º
25º
Focus – Prove the Triangle Sum
Theorem

The sum of the measures of the angles of a
triangle is 180.
mA  mB  mC  180
 Find the missing angle.
43
47º

Find the values of x, y, and z.
G
21
39
F
x - 11
x
y
J
z
H

All 3 angles are congruent.
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Has one right angle.
T
B
L
S
S
U

First tell me this, what is an acute angle?

An acute triangle has three acute angles.
50°
46°
72°
50°
58°
84°

What’s an obtuse angle?

An obtuse triangle has one obtuse angle.
X
S
A
135°
W
98°
M
V

A triangle with no congruent sides.
X
11”
28”
W
V
20”
Can we use tick/dash marks to denote congruence of sides in triangle XWV?

An equilateral triangle has three congruent
sides.
3’
3’
3’

Has at least two congruent sides.
F
J
M
E
A
O

An angle that is formed outside the polygon
by extending a side of the polygon past its
vertex.

The 2 interior angles of a triangle that are
nonadjacent to the exterior angle.

The measure of each exterior angle of a
triangle is equal to the sum of the 2 remote
interior angles.
Add These!
Get This!
120º
T
55º
J
U
120
35
L

Pg 134 – 135 #s 1-15, 24-28 all.