Section 4-1 Triangles and Angles

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

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

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

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

A B C 1

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

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