Learning goals: Teacher Facing Comprehend that a rotation by 180 degrees about a point of two intersecting lines moves each angle to the angle that is vertical to it. Describe (orally and in writing) observations of lines and parallel lines under rigid transformations, including lines that are taken to lines and parallel lines that are taken to parallel lines. Draw and label rigid transformations of a line and explain the relationship between a line and its image under the transformation. Generalize (orally) that “vertical angles” are congruent using informal arguments about 180 degree rotations of lines. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from 8.1 Rigid Transformations and Congruence, Grade 8.