1. Triangle Angle Sum Theorem, Triangle Exterior Angle Theorem
Objectives
State the triangle angle sum theorem and solve for an unknown angle in a triangle
Classify triangles based on measures of angles as well sides
State the triangle exterior angle theorem and solve for an unknown exterior angle of a triangle

2. Triangle Angle Sum Theorem
The sum of the measures of the angles of a triangle is 180°.
m∠A + m∠B + m∠C = 180 A B C
Ex: If m∠A = 30 and m∠B = 70;
what is m∠C ?
m∠A + m∠B + m∠C = 180
m∠C = 180
100 + m∠C = 180
m∠C = 180 – 100 = 80

3. Classifying Triangles

4. Exterior and remote interior angles
An exterior angle of a polygon is an angle formed by a side and an extension of an adjacent side
For each exterior angle of a triangle, the two nonadjacent interior angles are called the remote interior angles

5. Triangle Exterior Angle Theorem
The measure of each exterior angle of a triangle equals the sum of the measures of its two remote interior angles
m∠1 = m∠2 + m∠3
Ex: If m∠2 = 45 and m∠3 = 55, what is m∠1?
m∠1 = = 100