1. Section 4-1
Triangles and Angles

2. Using angle measures of triangles
Original angles of the triangle
Located inside the triangle!

3. Using angle measures of triangles
Angles that are
adjacent to the
interior angles
Located outside the triangle!

4. Triangle sum theorem
The sum of the measures of the interior angles of a triangle is B A C

5. 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.
Remote interior angles
Exterior Angle

6. A B C 1

7. A statement that can be proved easily using the theorem
Corollary to a theorem
A statement that can be proved easily using the theorem

8. Corollary to the triangle sum theorem
The acute angles of a right triangle are complementary. A B C