1. 4.1 – Apply Triangle Sum Properties
A triangle is a polygon with three sides. A triangle with vertices A, B, and C is called “triangle ABC”.

2. 4.1 – Apply Triangle Sum Properties
Example 1:
Classify Triangle ABC by its sides and by its angles.

3. 4.1 – Apply Triangle Sum Properties
Example 2:
Draw an obtuse isosceles triangle and an acute scalene triangle.

4. 4.1 – Apply Triangle Sum Properties
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. 4.1 – Apply Triangle Sum Properties

6. 4.1 – Apply Triangle Sum Properties
Example 3: Find an angle measure.
Find m<JKM

7. 4.1 – Apply Triangle Sum Properties
Example 4: Find an angle measure.
Find m<DEF

8. 4.1 – Apply Triangle Sum Properties
A corollary to a theorem is a statement that can be proved easily using the theorem.

9. 4.1 – Apply Triangle Sum Properties
Example 5:
The support for a skateboard ramp shown forms a right triangle. The measure of one acute angle in the triangle is five times the measure of the other. Find the measure of each acute angle.