Triangle Angle Sum Theorem, Triangle Exterior Angle Theorem

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

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

Classifying Triangles

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

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 = 45 + 55 = 100

Triangle Angle Sum Theorem, Triangle Exterior Angle Theorem