Angle Sum Theorem - the sum of the measures of the angles of a triangle is 180

Exterior Angle Theorem - The measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles

Third Angle Theorem - if two angles of one triangle are congruent to two angles of a second triangle, then the third angles of the triangles are congruent

Remote Interior Angle - in the figure below, a and c are remote interior angles

Included Angle - the angle formed by two given sides

Included Side - the segment of the triangle that is the side of two angles

*Explorations with GSP