5-3 Congruence Postulates for Triangles Proof Geometry

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

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.

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

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

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.

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 4. A D 2. BC EF 5. B E 3. AC DF 6. C F

What about Angle- Side – Side? http://www.youtube.com/watch?v=mpp6nMsWYrQ

Homework Hw p. 139 #1-3 + Worksheet