1. Notecards Unit 4
Triangle Properties

2. Classify Triangles by Sides
Definitions
Classify Triangles by Sides

3. Classify Triangles by Angles
Definitions
Classify Triangles by Angles

4. Definitions Interior and Exterior Angles
When the sides of a polygon are extended, other angles are formed. The original angles are the interior angles. The angles that form linear pairs with the interior angles are the exterior angles.

5. Triangle Sum Theorem Theorem
The sum of the measures of the interior angles of a triangle is 180°. A
B C

6. Exterior Angle Theorem
The measure of an exterior angle of a triangle is equal to the sum of the measures of the two nonadjacent interior angles. A
B C D

7. Corollary to Triangle Sum Theorem
The acute angles of a right triangle are complementary. A
B C

8. Side Angle Relationships in a Triangle

9. Definition of Midsegment
A midsegment is a segment that connects the midpoints of two sides of a triangle. Every triangle has three midsegments.
Line segment BD is a midsegment
of triangle AEC

10. Midsegment Theorem Theorem
The segment connecting the midpoints of two sides of a triangle is parallel to the third side and is half as long as that side.
BD = ½ AE
BD is parallel to AE

11. Triangle Inequality Theorem
The sum of the lengths of any two sides of a triangle is greater than the length of the third side. A
AB + BC > AC
BC + AC > AB
B C AC + AB > BC