1. Parallel Lines and the Triangle Angle Sum Theorem
Geometry 3-3

2. Exterior Angle – The angle formed outside the triangle, and along a side as shown
Triangle Term

3. Exterior Angle –
Exterior
Angle
Triangle Term

4. Exterior Angle – Six different exterior angles can be formed for a triangle
Triangle Term

5. Investigation Supplies Scissors Printer Paper
Draw two different shaped triangles with a ruler (be creative)
Cut them out with a scissors
Investigation

6. With ONE of the triangles, tear off the corners of the triangles
Arrange the angles so they are adjacent
What do you observe?
Investigation

7. With the remaining triangle, tear off two corners of the triangles
Arrange the torn corners in the place of an exterior angle to the remaining angle
What do you observe?
Investigation

8. What we have learned Triangle Sum Theorem
The sum of the measure of the interior angles of a triangle is 180°
What we have learned

9. Alternate Interior Angles
Triangle Sum Theorem
How can this be proven with parallel lines? y° Z°
Alternate Interior Angles
What we have learned

10. What we have learned Exterior Angle Theorem
The measure of an exterior angle of a triangle is equal to the measure of the two non-adjacent interior angles
What we have learned

11. Practice Problems

12. m1=75°
m6=40°
m2=55°
m7=75°
m3=55°
m8=65°
m4=40°
m9=115°
m5=140°

13. X=23
Exterior Angle = 100°

18. mt = 62°
mv = 118°
mw = 37°

22. Pages 135 – 138
6 – 11, 16 – 22 even, 27, 28, 33, 36, 49
Homework