The document provides a lesson on triangle measures including the triangle sum theorem which states that the sum of the interior angles of any triangle is 180 degrees. It gives examples of using the triangle sum theorem to find missing angle measures. The lesson also covers exterior angles of triangles and states that an exterior angle is supplementary to its opposite interior angle.

1. Warm Up
Place the date in the top right of your paper.
Sept. 10, 2012
If <3 is 75 ̊, find the measures of the other angles.
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2. Activator
Exploring Triangles
Watch me Fold for Understanding!

3. Triangle Measures

4. Triangle Measures
Interior Angles

5. Triangle Measures
Interior Angles of a Triangle
Triangle Sum Theorem
All angle measures inside the triangle
(interior angles) added together equal
180 ˚. a
c
m<a +m<b + m<c = 180 ˚
b
Let’s Practice

6. Triangle Measures
What is the value of x?
35 ˚
40 ˚ x
* This figure is not drawn to scale.

7. Triangle Measures
What is the value of x?
35 ˚
40 ˚ x
35 + 40 + x = 180
75 + x = 180
x = 105

8. Triangle Measures
What is the value of x?
45 ˚
90 ˚ x
* This figure is not drawn to scale.

9. Triangle Measures
What is the value of x?
45 ˚
90 ˚ x
45 + 90 + x = 180 ˚
135 + x = 180 ˚
x = 45

10. Triangle Measures
Exterior Angles

11. Triangle Measures
a
Exterior Angle
b c
From the above figure what can you state about
<c and the exterior angle?

12. Triangle Measures
a
Exterior Angle
b c
From the above figure what can you state about
<c and the exterior angle?
They are supplementary.

13. Triangle Measures
a
Exterior Angle
b c
Let’s Explore the Measures!
Click the link

14. Triangle Measures
a
Exterior Angle
b c
More Examples
Click the link
Practice!

15. Closing
Human Paragraph
I need five volunteers to sum up the lesson!