1. 5-3 Congruence Postulates for Triangles
Proof Geometry

2. A well known Triangle Theorem
The sum of the interior angles in a triangle is 180˚.
Triangle Sum Theorem:
We will leave the proof until later

3. Exterior Angle of a Triangle
3 is called an exterior angle of the triangle
An exterior angle is created by lengthening one of the sides of the triangle.
An exterior angle forms a linear pair with one of the angles of the triangle.
The other two angles of the triangle are called the remote interior angles.

4. Exterior Angle formal Defintion
If C is between A and D, then BCD is an exterior angle of ABC

5. Every triangle has 6 exterior angles.2 1 3 X 4 6 5 X
X = not exterior angles

6. Exterior Angle Theorem
The measure of the exterior angle in a triangle is equal to the sum of the measures of the remote interior angles.

7. Congruent Triangles  ABC  DEF
If all six pairs of corresponding parts (sides and angles) are
congruent, then the triangles are congruent.
Sides are
congruent
Angles are
congruent
Triangles are
congruent If
and
then
 ABC  DEF
1. AB DE
A D
2. BC EF
B E
3. AC DF
C F

9. What about Angle- Side – Side?

10. Homework
Hw p. 139 #1-3 + Worksheet